AceBoard is a hosted forum where each forum gets a subdomain off of a domain such as aceboard.com There are several very popular French forums using this software. To find forums you may choose to use the search I mention above the AceBoard footprints. The footprints show how you can target AceBoard forums in different languages.

"AceBoard Free Forum" "Download Premium Web Templates!" keyword
"Ce forum pour votre site ?" "AceBoard Forum Gratuit" keyword
"Apri un forum gratuitamente!" "AceBoard Forum Gratuito" keyword

Advanced Electoron Forum (AEF) is a free PHP forum with standard forum features. The Advanced Electron footprints below help you find this forum, the registration page, specific versions of it and also there is an example of how you can target a keyword as well.

"Powered by AEF"
"Powered by AEF" inurl:index.php?act=register
"Powered By AEF" "Electron Inc."
"Powered By AEF" "Electron Inc." keyword
"Powered By AEF" "Registered members"
"Powered By AEF 1.0.8"
"Powered By AEF 1.0.6"

ASP Playground is Forum software developed for webmasters using ASP.NET AJAX framework and SQL Server database. The ASP Playground.NET footprints below will help you target forums, the registration pages and specific releases.

"ASPPlayground.NET Forum Commercial Version" keyword
"ASPPlayground.NET Forum Commercial Version" keyword inurl:/register.aspx
"ASPPlayground.NET Forum Commercial Version" keyword inurl:/register.asp
"Forum Software powered by ASP Playground Advanced Edition" keyword
"Forum Software powered by ASP Playground Advanced Edition" keyword inurl:/register.aspx
"ASPPlayground.NET Advanced Edition" keyword
"ASPPlayground.NET Advanced Edition" keyword inurl:/register.aspx
"ASPPlayground.NET Forum Commercial Version 3.8" keyword
"ASPPlayground.NET Forum Commercial Version 3.9" keyword
"powered by ASP Playground Advanced Edition 2.3" keyword
"powered by ASP Playground Forum SQL v1.99.24 SP4" keyword
"ASPPlayground.NET Advanced Edition 2.4.5 ANSI" keyword
"ASPPlayground.NET Advanced Edition 2.5.5 Unicode" keyword

bbpress is forum software from the makers of wordpress. Its a simple easy to install and use forum. The first bbPress footprint is pretty basic. The second shows how you can target a specific release.

"is proudly powered by bbPress" keyword
"is proudly powered by bbPress 0.9.0.6-2442" keyword

The Beehive Forum is a PHP forum that even includes dyslexia support. Here are 2 Beehive footprints I made that work pretty good at finding Beehive forums and eliminating junk results.

"Project Beehive Forum" "registered members"
"Project Beehive Forum" "registered members" keyword

Burning Board is discussion board software that is used to create communities for everyone. I've included several Burning board footprints in different languages and also targeting different releases and the registration page.

"Forum Software: Burning Board" "developed by WoltLab" keyword
"Forum Software: Burning Board" "developed by WoltLab" inurl:/register.php
"Forensoftware: Burning Board" "entwickelt von WoltLab" keyword
"Forum Software: Burning Board® 3.1.3, developed by WoltLab® GmbH" keyword
"Forensoftware: Burning Board 2.3.2, entwickelt von WoltLab GmbH" keyword
"Forum Software: Burning Board 2.3.6, Developed by WoltLab GmbH" keyword
"Forensoftware: Burning Board 2.3.6, entwickelt von WoltLab GmbH" keyword
"Forum Software: Burning Board 2.3.6 pl2, Developed by WoltLab GmbH" keyword
"Forensoftware: Burning Board® 3.1.3, entwickelt von WoltLab® GmbH" keyword

Discuz! powers many international forums. I've included several Discuz! footprints targeting different releases and registration pages.

"Powered by Discuz!"
"Powered by Discuz!" keyword
"Powered by Discuz!" inurl:register.php
"Powered by Discuz! X1.5" keyword
"Powered by Discuz! 6.0.0" keyword
"Powered by Discuz! 7.0.0" keyword

E-blah is a forum made using the Perl. The last time it was updated was in release 10.3.6 on August 2008. Sometimes finding an old abandoned forum can be a goldmine for placing links as they aren't moderated anymore.

Here are some E-Blah footprints. The second footprint will take you straight to the registration page and the third and fourth target specific versions of E-blah.

"powered by E-Blah" keyword
inurl:"Blah.pl?v-register" keyword
"Powered by E-Blah Forum Software 10.3.6" keyword
"Powered by e-blah Platinum 5" keyword

ExpressionEngine is forum software and 3 ExpressionEngine footprints I use are below.

"powered by expression engine" keyword
"powered by expressionengine" keyword
"ExpressionEngine Forums" keyword

People using Joomla have a forum named Fireboard available to them that uses the Joomla database. The Fireboard footprint I use is below.

"Powered by FireBoard" keyword

FluxBB is a forum that claims they are fast and light. You can find these forums using my FluxBB footprints below. Add a keyword to target your search or add a version number to refine your search as in these example footprints.

"powered by fluxbb" "Newest Registered"
"powered by fluxbb" "Newest Registered" keyword
"Powered by FluxBB 1.3"

The Fruit Show Forum is very basic. Seriously, it has very minimal features and I didn't find many forums out there using this software. Here is a Fruit Show footprint.

"Powered by FruitShow"

Fast Uncompromising Discussion Forum (FUDForum) is written in PHP and its last release was in late 2010. Some FUDForum footprints are listed below.

"powered by: fudforum"
"powered by: fudforum" keyword
"Powered by: FUDforum 3.0.2." keyword
"Powered by: FUDforum 3.0.0." keyword
"Powered by: FUDforum 2.8.0." keyword
"FUDforum Bulletin Board Software' keyword

FuseTalk has been around for over 10 years so there are plenty of forums out there using this software. I find the first and second FuseTalk footprints work the best. The rest are examples of how to find specific releases of FuseTalk.

"users are registered to" "FuseTalk Inc."
"users are registered to" "FuseTalk Inc." keyword
"FuseTalk Basic Edition" "FuseTalk Inc." keyword
"FuseTalk Basic Edition v3.2" "FuseTalk Inc." keyword
"FuseTalk Enterprise Edition v3.2" keyword
"FuseTalk 4.0" "FuseTalk Inc." keyword
"FuseTalk Enterprise Edition v4.0" "FuseTalk Inc." keyword

IceBB seems to have a few forums on the web but when I go to their company website their account is suspended making me think they no longer are interested in supporting their software. The first IceBB footprint works the best and gets rid of some lousy results. You may wish to run your search without a keyword as there aren't a ton of these forums out there.

"Powered by IceBB" "XAOS Interactive"
"Powered by IceBB" "XAOS Interactive" keyword
"powered by icebb"
"powered by icebb" keyword

IGN Message boards seem to be either hosted at boards.ign.com or by webmasters at their own url. There are 2 ways to find them. You can either use the search link I've provided or the IGN Footprints under it

IGN Board Search
"IGN's enterprise databases running Oracle, SQL and MySQL are professionally monitored"
"IGN's enterprise databases running Oracle, SQL and MySQL are professionally monitored" keyword

ikonBoard is forum software that focuses on building a community. There are over 1 million forums using this software. I've included several ikonBoard footprints below.

"Powered by Ikonboard"
"Powered by Ikonboard" keyword
"Powered by Ikonboard 3.1.1" keyword

Invision Power Board is forum software that's pretty popular so of course we're going to need a couple of footprints for it as well. Lets start out with your basic footprint:

"Powered by Invision Power Board" "keyword phrase"
or maybe you're looking for a specific version
"Invision Power Board v2.1.7" "keyword"
To find the newer version as of today I would try this
"Community Forum Software by IP.Board" "keyword phrase"
Sometimes you want a footprint to go straight to the registration page so you can hopefully become a member and get in some backlinks.
"Community Forum Software by IP.Board" inurl:section=register
You can add a keyword as well in the above line but sometimes people don't really care about what the forum is about. They want to tell the world about their site :) Hope that gives you a bit to work with and helps you to create some of your own footprints.

javaBB is forum software written in java. They do custom versions of their forum for large clients. A lot of the forums using this software seem to be in Portuguese. I played around a bit to come up with some good javaBB footprints. The first one works pretty good and the third footprint isn't too bad.

"Powered by JavaBB 0.99" "Devmedia"
"Powered by JavaBB 0.99" "Devmedia" keyword
"powered by javabb" -footprints -scrapebox

Jive Community software has an expensive license so there aren't as many of their forums out there. I've developed a Jive footprint that I'll admit isn't that stellar, but about every 4th result will be a Jive forum.

"powered by Jive" "community software"
"powered by Jive" "community software" keyword

MesDiscussions is forum software that uses PHP/MySQL. It seems to cater to people using the French language as all the forums I found using this software were in French. These MesDiscussions.net footprints work pretty good.

"Forum MesDiscussions.Net" "Doctissimo Software"
"Forum MesDiscussions.Net" "Doctissimo Software" keyword

miniBB is pretty cool forum software. It lets you compile a release that is specific to your needs. The first miniBB footprint is the best as it filters out a bunch of non-forum sites. The second footprint also works but you will get a lot more unrelated websites. You can always add a keyword as in the third query to target forums related to the site you wish to backlink to.

"powered by forum software minibb" -footprint -scrapebox -"powered by phorum"
"powered by forum software minibb"
"powered by forum software minibb" keyword

MyBB is straightforward and is pretty typical forum software. I've included a few MyBB Footprints below.

"Powered By MyBB" "members registered"
"Powered by MyBB"
"Powered by MyBB" keyword

Phorum is a PHP / MySql forum that was developed in 1998. It is a very simple looking forum. Below are the Phorum footprints I've developed. The first will find many forums, the second will find forums related to your keyword, and the third will find the registration page of this type of forum. The 4th and 5th Phorum footprints quickly find forums due to them being in the url.

"This forum is powered by Phorum."
"This forum is powered by Phorum." keyword
"This forum is powered by Phorum." inurl:register.php
phorum/list.php
phorum/posting.php

phpBB is forum software (aka bulletin board software) which is similar to vBulletin. The main difference between the two forums is that phpBB is free and vBulletin is software that you pay for. Some people would argue that because you have to pay for vBulletin that the websites using it would be higher quality. But I can assure you that are are a lot of great phpBB sites out there that are worth getting a link from.

The most basic way to find a phpBB forum related to your keyword is to use this footprint.
"powered by phpbb" keyword
If you want to get results that use keywords similar to your keyword then try a tilde ~ in front of your keyword like this
"powered by phpBB" "~keyword"
phpBB has been through several releases so you can also target a specific release using one of these footprints.
inurl:phpbb "keyword phrase"
inurl:phpbb2 "keyword phrase"
inurl:phpbb3 "keyword phrase"
or if you want to use the tilde trick then doing something like this
inurl:phpbb3 ~"keyword phrase"
inurl:phpbb3 ~keyword

PunBB is forum software. Here are a few footprints I created to find forums using PunBB. I throw in a few examples of how you can use other languages in your footprints to unearth even more forums to place links on.

"powered by PunBB" keyword
"PunBB ile güçlendirildi" keyword
"supported by Informer Technologies, Inc." keyword
"unterstützt von Informer Technologies, Inc." keyword

Quicksilver forums have been around a while and have recently updated their software in 2011. If you become a member of these forums they allow a backlink in the members list that can be seen without being logged into the forum. Here are my Quicksilver Forums Footprints.

"Powered by Quicksilver Forums" "Based on MercuryBoard"
"Powered by Quicksilver Forums" "Based on MercuryBoard" keyword

SEO-Board is free forum software written in PHP. It is claimed to be SEO friendly. The first SEO-Board footprint will work best and you can add a keyword as in the remainder of the examples. The last footprint shows how to target a specific release.

"powered by seo-board" "forum has" "registered members"
"powered by seo-board" "forum has" "registered members" keyword
"powered by seo-board" keyword
"Powered by SEO-Board 1.1.0" keyword

Simple Machines Forum is yet another free PHP and mySQL type of community software that is great for forums.
Here are a couple of the footprints I know of that can quickly find you SMF forums.

"powered by SMF" keyword
"powered by SMF 1.1.13" "keyword phrase"
"simple machines llc" keyword
You can see I've used a version number 1.1.13 in one of the examples. This of course can be changed to any release number if you are targeting forums of a certain release.

Snitz Forums 2000 has been around for a while. They haven't updated their code for a few years though. The following Snitz footprints will help you locate these forums. The first two Snitz Forums footprints work well. The third footprint is an example of how you can target certain versions of the software.

"Snitz Forums 2000" "Please welcome our newest member" keyword
"Powered By: Snitz Forums" keyword
"Powered By: Snitz Forums 2000 Version 3.4.07" keyword

Telligent is community software with forums and other applications integrated with it. The first Telligent footprint I've shown below works the best and looks for the signup page. Once you have figured out several urls you can also look at the html source code and find specific releases of the Telligent Community or Community Server as the last 6 footprints show.

"inurl:CreateUser.aspx?ReturnURL=" keyword
"Telligent Community (Build: 5.5.133.9594)" keyword
"Telligent Community (Build: 5.5.134.11785)" keyword
"CommunityServer 2008 SP1 (Build: 30619.63)" keyword
"CommunityServer 2.1 SP1 (Build: 61025.2)" keyword
"CommunityServer 2008 SP2 (Build: 31104.93)" keyword
"CommunityServer 2.0 (Build: 60217.2664)" keyword

UBB is forum software with portal and photo gallery functionality. They've been around since 1997 and many popular forums can be found using their software. I have created three UBB footprints. The 3rd footprint works awesome at finding registration pages. Try the 3rd UBB footprint without using a keyword as well.

"Powered by UBB.threads" keyword
"Powered by UBB.threads™ 7.5.5" keyword
inurl:/ubbthreads.php/ubb/newuser.html keyword

UBB has an integrated photo gallery and portal allowing you to create your website to include a forum. Included below are some UBB.threads footprints. I did a post on this forum before but here are a few extra footprints.

"powered by ubb.threads"
"powered by ubb.threads" keyword
"powered by ubb.threads" "Who's Online"
"powered by ubb.threads" inurl:newuser
"Powered by UBB.threads™ 7.5.6"
"Powered by UBB.threads™ 7.4.2"
"Powered by UBB.threads™ 7.5.5"

Unclassified NewsBoard (UNB) is free forum software written written in PHP. The latest version was released in 2007 and there has been a development version available since 2010. The following UNB footprints will help you find these forums. There haven't been many releases of this forum so I haven't included any release specific Unclassified NewsBoard footprints.

"powered by the Unclassified NewsBoard software" "by Yves Goergen"
"powered by the Unclassified NewsBoard software" "by Yves Goergen" keyword

UseBB is an open source PHP forum that is freely available. UseBB footprints are included below to help you find these forums. The second footprint uses a keyword to target the search.

"My Community is powered by UseBB 1 Forum Software"
"My Community is powered by UseBB 1 Forum Software" keyword

Vanilla is forum software that is made to integrate easily with other website apps like blogs. It is open source and free. Here are my Vanilla footprints.

"Powered by Vanilla" "Howdy, Stranger!"
"Powered by Vanilla" "Howdy, Stranger!" keyword

vBulletin is forum software and has one of the easiest footprints to use. Here are some examples.

"Powered by vBulletin"
"Powered by vBulletin" "keyword phrase"
"Powered by vBulletin" 4.1.1 "keyword"
The number 4.1.1 above is just a release number. Others include 1.1.5, 3.6.1, 3.8.4, etc. Some people target certain releases for back linking purposes as older releases may have less security features or possibly don't block links with a no-follow attribute.

Viscacha is free forum software that also allows you to setup a homepage. Viscacha footprints I've created are below.

"Powered by Viscacha" "The Viscacha Project"
"Powered by Viscacha" "The Viscacha Project" keyword
"Powered by Viscacha" "The Viscacha Project" inurl:register.php
"Powered by Viscacha 0.8.1" "The Viscacha Project"

XenForum is forum software that needs to be purchased. It is said to be SEO optimized and a challenger to vBulletin. My XenForo footprints are below.

"Forum software by XenForo" "XenForo Ltd."
"Forum software by XenForo" "XenForo Ltd." keyword

XennoBB is forum software that is a bit older. The domain name associated with it has been bought by someone else so its likely kind of dead. Regardless, you may find some good backlinking opportunities at some of the abandoned forums. Below are a general XennoBB Footprint and a keyword specific version.

"powered by XennoBB" "Xenno Group"
"powered by XennoBB" "Xenno Group" keyword

eXtreme Message Board (XMB) is written in PHP and its most recent version was released in 2009. The XMB footrpints below will get you started finding XMB forums that are related to your keyword as well as targeting specific releases of XMB.

"Powered by XMB"
"Powered by XMB" keyword
"XMB Forum Software" "The XMB Group" keyword
"Developed By The XMB Group" keyword
"Powered by XMB 1.9.11" keyword
"Powered by XMB 1.9.5 Nexus (Final)" keyword

Yet Another Bulletin Board (YABB) was written in PERL and is free BB forum software. Here are some Yabb footprints to help you find these forums.

"powered by yabb"
"powered by yabb" keyword
"Powered by YaBB SE" keyword
"Powered by YaBB 1 Gold - SP 1.3.1!" keyword
"Powered by YaBB 1 Gold" keyword
"Powered by YaBB 2.3.1!" keyword
"Powered by YaBB 2.4!" keyword

Yet Another Forum (YAF) is a free open source forum that has commercial options available. YAF Footprints are below.

"powered by yaf" "Yet Another Forum.NET"
"powered by yaf" "Yet Another Forum.NET" keyword
inurl:yaf_rules.aspx
"Powered by Yet Another Forum.net version 1.9.1.8 (NET v2.0)"
"Powered by YAF 1.9.5 RC1"
"Powered by YAF 1.9.4 RC1"

Yuku calls their forums "social communities" and they have tons of them. They are subdomains of yuku.com and the older Ezboard forums are being upgraded to Yuku. I have included one Yuku footprint and one link below to help you find these forums.

"Yuku. All rights reserved." keyword
You can also go to Yuku's search page that helps you find their forums.
Yuku Search