Although much of the Android code is open source, the full eco-system is less free than some would have hoped for. Not only are many of the hardware drivers non-free and proprietary, many of the default applications are also non-free and also requires sign-in.
The list of free software Android applications is therefore a welcome contribution. In addition, there is an alternative free market application and repository (APK ownload), which gives access to the other free apps. It works as the built-in Google market, but requires no sign-in, and neatly lists the license used for each application. For the developers that offers different version, one can download and install not only the latest, but several different version of the same software. Finally, it allows the user to add additional repositories, just as one would do on a desktop GNU/Linux distro.
Amongst the free apps is the calendar replacement aCal, which uses the CalDAV protocol. Combined with the DAViCal server, it might be and interesting replacement for Google calendar. The support in Thunderbird looks a lot more promising.