This page will contain user-contributed add-ons for Mixxx.
For extra skins, check out the skins subforum on the Mixxx forums.
If you write an audio playback plugin, here's a good place to link to it.
Below is where Mixxx will look for plugins on each OS:
Linux:
Windows:
OSX:
Tell Mixxx to look for plugins in additional locations by calling it with the –pluginPath argument (for instance, if one wants to be able to play m4a files from a trunk build without installing, call ./mixxx –pluginPath ./linux_build/plugins/linux_build, changing linux_build to the appropriate directory name as necessary). As many –pluginPath arguments may be specified as necessary.