The Free Software Foundation is fundraising for Replicant, its fully free and open version of the Android operating system, in which all the restrictively licensed elements have been replaced with functionally equivalent components made from free software. I've just donated -- I love the idea of fully free OSes; they are frequently the best of breed, and even when they lag, they represent huge competitive pressure on proprietary and semi-proprietary vendors to be more free and open.
While most of Android is already free software, device manufacturers distribute the OS with some key nonfree parts. Those parts are in the layer of Android that communicates with the phone or tablet hardware, such as the WiFi and Bluetooth chips. In addition, every commonly available Android device comes pre-loaded with a variety of proprietary applications running on top of the operating system. Replicant seeks to provide all of the same functionality using only free software.
Users of Replicant have a full suite of free software mobile-optimized applications at their fingertips through F-Droid, Replicant's default app repository. F-Droid isn't just for Replicant -- it works on all Android-based systems, and the FSF recommends it as a replacement for Google Play store.
Mobile operating systems distributed by Apple, Microsoft, and Google all require you to use proprietary software. Even one such program in a phone's application space is enough to threaten our freedom and security -- it only takes one open backdoor to gain access. We are proud to support the Replicant project to help users escape the proprietary restrictions imposed by the current major smartphone vendors. There will still be problems remaining to solve, like the proprietary radio firmware and the common practice of locking down phones, but Replicant is a major part of the solution.