Helping with MoinMoin development
develop new extensions (macros, actions, processors, parsers)
run the development version and help testing the new features
test MoinMoin on a certain platform, or with certain Python versions
help with the translation efforts, especially adding new languages
help developping new themes, CSS and icons
In any case, you should subscribe to the MoinMoin Developer List. More information on MoinMoin source code and other developer issues can be found in the MoinMoin main wiki, on MoinDev and its subpages.
The distribution contains a "contributions" directory for 3rd party extensions that are not made part of the official distribution. This directory contains extensions contributed by MoinMoin users and that are considered either too exotic or need too much work to be integrated into the core sources. Another reason of not adding them is that modules in the core have to be maintained when structural changes happen, which is a constant burden.
Thus, these sources are here for you to try them out and take advantage of a feature someone found useful enough to write code for, but you cannot expect that they always work with the current distribution. Contributors are encouraged to send updates...
Other sources of user contributions are linked from MoinMoinExtensions.