sage-combinat
sage-combinat is a collection of experimental patches (i.e. extensions) on top of [http://www.sagemath.org/ sage], developed by a community in algebraic combinatorics. Its main purpose is to improve sage as an extensible toolbox for computer exploration, and foster code sharing between researchers in this area. The intent is that most of those patches eventually will get integrated into sage as soon as they are mature enough, with a typical short life-cycle of a few weeks.
sage-combinat is likely to become the natural successor of [http://mupad-combinat.sf.net MuPAD-Combinat]. See in particular: [http://mupad-combinat.sf.net/Wiki/Sage].
Anyone interested in sage-combinat is encouraged to join our mailing list: [http://groups.google.com/group/sage-combinat-devel].
The collection of patches is managed using a [http://sage.math.washington.edu:2144/ patch server] (mercurial queues). Although an occasional contributor can simply send such a patch to the [http://groups.google.com/group/sage-combinat-devel mailing list] anyone contributing regularly should use the patch server. Some detailed instructions are at [http://wiki.sagemath.org/combinat/Mercurial].
Thanks to Jason, there is a page who sumarize all the weirdness. I think we can start from that to make a TODO list : [http://wiki.sagemath.org/combinat/Weirdness].