Just a quick random list of tools/online apps to support an online community.
Not a single claim made for this: comprehensiveness, quality, accuracy. (Sorry!!)
Link, date, plus a quick quote from the site, plus any comment. Often want such a list to refer to. (Will I remember it is here?) - Derek

  • Social Go. 4/3/09
    QUOTE: Build a website to blog, chat and also make money. It is free to get going and ridiculously easy to use. Build a vibrant online community now with SocialGO.
    Comment: Free version may be add supported? http://www.socialgo.com/free-premium.htm
  • Dolphin. 4/3/09
    QUOTE: Best. Community Software. Ever. YouTube, MySpace, Odeo, Flickr, Match and Facebook - all in one, customizable and under your full control. You're limited only by your imagination - not by software. Dolphin Smart Community Builder is a universal, free, open source software that allows you to build any kind of online community. With a huge variety of features & options, you can quickly develop your very unique and successful website.
    Comment: tons of associated community sites, has an ajax based forum as well called Orca.
  • Elgg. 4/3/09
    QUOTE:Elgg is an open, flexible social networking engine, designed to run at the heart of any socially-aware application. Building on Elgg is easy, and because the engine handles common web application and social functionality for you, you can concentrate on developing your idea. Elgg is open source. That means, when you use Elgg, you have the benefit of being part of a large developer community, with the security and stability that hundreds of eyes can provide. It's also headed and used by Curverider and its partners, so you can be assured that it's in commercial use and will cope with the demands of a popular application.
    Comment: open source
  • Ning. 4/3/09
    QUOTE: "What makes your own social network on Ning special? It's yours. Your brand and visual design. Your choice of public or private. Your very own members"
    Comment: Hosted
  • Jive 4/3/09
    QUOTE: "Jive Software is the leader in business social software - software that catalyzes relationships between employees, customers, and partners. By leveraging the best aspects of web 2.0 technologies, built from the ground-up to address the scalability, integration, and usability needs of today's biggest companies, Jive's Clearspace software can help grow your market, unite your team, and ultimately maximize your selling success. Jive is the only company that can provide a proven end-to-end solution that connects everyone from the exec team to field teams, from channel partners to potential buyers"

Other lists

Large list from 2007: Social Networking Articles
Blog Post: Don Hinchecliffe's list.
List of Open source CMS platforms (PHP/mySQL): http://php.opensourcecms.com/