- MetaFilter itself, where you can find the list of all current "best of the Web" posts and the SideBar, is also known as MeFi or "the blue" based on its hex color, #006699.
- MetaTalk, an area of the website specifically devoted to issues that concern the website itself. Also known as MeTa or the "the grey".
- Ask MetaFilter, where users ask the community a variety of questions, taking advantage of the experience and knowledge of the other members. Also known as AskMe or "the green".
- MetaFilter Projects, where people post links to sites they've worked on (the official way to skirt the "no self links" rule)
- MetaFilter Music, where you can post music you've worked on.
- MetaFilter Jobs, where jobs are posted.
- MetaFilter IRL, where you can post meetups, concerts, art openings, and other events MetaFilter members are involved in and other members can participate in.
- MetaFilter Chat is a group space where MetaFilter members can talk to each other in real time.
A number of possible sub-sites have been proposed over the years, but none have actually been created.
Thoughts about MetaFilter
What is MetaFilter?
From the OED: "In Greek, the Meta prefix is joined chiefly to verbs and verbal derivatives; the principal notions which it expresses are: sharing, action in common; pursuit or quest; and, especially, change (of place, order, condition, or nature)".
And, from Merriam Webster: A filter is a "porous material through which a liquid or gas is passed in order to separate the fluid from suspended particulate matter".
So MetaFilter can be thought of as a shared pursuit or quest to separate the particulate matter of the web from the ubiquitous fluid it's suspended in. Put simply, it's a collaborative effort to point out (and discuss) the interesting stuff on the web.
MetaFilter runs on a ColdFusion engine written by Matt Haughey. The source isn't available. If you'd like to run your own MetaFilter-esque website, there are plenty of open source engines that fulfil many of the features (plus more, in some cases) that MetaFilter offers. (See also: Mefi Clones)
Additional MetaFilter Information
You can find details regarding MetaFilter's RSS feeds at RSSFeeds.