MetaFilter itself is written in ColdFusion and runs on IIS. This is not highly portable and to date MattHaughey has not released the code (although he has tweaked it for other communities). A search for an easy-to-use alternative began as early as 2001. By early 2003 there were three alternatives for those seeking to host their own discussion community using software with the MetaFilter interface and behavior, and available for common webhost configurations.
Sites running variations of the original MeFi code include [SportsFilter] and [BlogRoots].
[FreeFilter] is written in Perl. It is open source, and the work of Peter Cooper (MeFi ID: [wackybrit]). Sites running FreeFilter include [FilmFilter]. [FreeFilter] is no longer being updated but is still available for downloading.
[MetaPhilter] (the [old domain name] appears to have lapsed) is written in PHP, open source, and the work of Jack Driscoll (MeFi userid unknown). There is a conversion tool for FreeFilter. Sites running MetaPhilter include [GamesFilter], [BookFilter], [MusicFilter], [LibertyFilter], [GyrlFilter], [MonkeyFilter], and some personal blogs.
[Phpilfer] is written in PHP, open source, and the work of [holloway]. Update: May 1st 2004 -- Phpilfer has a new release
[Whedonesque] (a.k.a. [BuffyFilter]) is written in Perl/mySQL, and is the work of [prolific]. It is officially sanctioned by [mathowie], who may have consulted to help tweak the code a bit. Package appears to be not available on site