Commu is an interface to “draw” commutative diagrams with PGF/TikZ (here is a gallery). PGF/TikZ wasn’t designed to draw commutative diagrams (for example, it doesn’t handle automatically the space between objects), anyway it can be used with
small effort, particularly if there’s an interface that does all the trivial stuff. Moreover, the results are more appealing than the one you could have using other packages.
However, some constructions are almost hacks: e.g., the Equal and Element (which should replace
\mapsto); the isomorphism decorations is simply a
\widetilde with an arbitrary length.
Here’s the mandatory screenshot of the unergonomic (but more or less self explanatory) GUI, plus a diagram, with almost everything you can do with Commu.
The last version is 20080916, released the 16th September, 2008. You can download it here.