Some information about the contents of the directories:

-libmnemosyne: the main python library that does all the heavy lifting common
 to all the frontends.
-example_plugins: some example plugins for libmnemosyne.
-example_scripts: some example script for libmnemosyne.
-script: very simple frontend, makes it easy to interface with libmnemosyne
 in scripts.
-pyqt_ui: the Qt frontend, written in Python, for use on desktop machines
 under Windows, Linux and OSX.
-ppygui_ui: the PocketPyGui frontend, for use on Windows Mobile.
-webserver: the webserver frontend, to do reviews in your browser.
-UDP_server: talk libmnemosyne over the UDP protocol. Useful if you want to
 write a frontend in a language other than Python, and if you have the option
 to run a separate process.
-embedded_in_C: embeds libmnemosyne in a C application. Useful if you don't
 have the option of running separate processes on your client machine.
-sl4a: python Android app using a locally running webserver.
-cle: python code for interfacing with a frontend written in different language
 using the CLE library (e.g. interfacing with Java for the native Android 
 client).
-android: Java UI frontend