sitescode

Dolphin

Cross-platform

Build your own social network, dating site or online club with free, powerful open-source software that you host, control, customize and extend. (CC)

Elgg

Cross-platform

Elgg is an open, flexible social networking engine, designed to run at the heart of any socially-aware application. (GPL)

Lovd by Less

Cross-platform

Built with Ruby on Rails, Lovd is a social networking solution that has everything you need to build your community. (MIT)

Pligg

Cross-platform

Pligg CMS provides social networking software that encourages visitors to register on your website so that they can submit content and connect with other users. (AGPL)

Popularity: 8% [?]

PhPBB

phpBB is one of the most popular forum softwares. With phpBB you can customize with mods and you can stylize your forum. For a fully Modded phpBB forum with about 500 different mods that all have been fully tested click

Vanilla

Vanilla is a lightweight open source forum that was developed by Mark O’Sullivan using PHP and MySQL. Vanilla comes loaded with extensions, and you can customize the forum with your own add-ons.

YetAnotherFroum.Net

YetAnotherForum.NET is a Open Source forum or bulletin board for web sites running ASP.NET. YetAnotherForum.NET is fully coded in C# ASP.Net and uses Microsoft SQL Server. It comes with all the standard forum features and even WYSIWYG editors.

YaBB

YaBB is an Open Source forum system (bulletin board, message board) written in Perl. This system is the first and most popular open-source perl forum software and it runs very fast.

IceBB

IceBB is an open-source forum solution powered by PHP and MySQL. IceBB is written with the prototype and scriptaculous frameworks and the code output is very clean. IceBB has mostly all the same features as some of the paid forums but it even has an RSS feed.

Wp-Forum

WP-Forum is a simple discussion forum plugin for WordPress. It has three themes that you can choose from and is a simple solution if you have a WordPress powered site.

MiniBB

miniBB is an open source message board script written in PHP. miniBB is a lightweight and compact alternative to phpBB. With miniBB you can customize the software with add-ons and it is Search Engine Optimized.

SMF

SMF is a free professional grade forum software that actually isn’t open source. SMF has loads of features with a great community and tons of free modifications.

Some another  Forum Script    are Also  good  to use

Drupal Forum

BBPress

SEO Board

FudForum

PUNBB

FluxBB

Beehive Forum

Phorum

Extreme Message Board

Popularity: 100% [?]