The projects there have been described in my corresponding posts about them: http://arclanguage.org/submitted?id=fallintothis.
There's also the community-wide repo dubbed "Anarki" for alterations to Arc: http://github.com/nex3/arc/.
A lot of posts here are about people's projects, so have a poke around (e.g., aw's stuff at http://awwx.ws/ or evanrmurphy's http://tryarc.org/).
