XCSoar is a very nice free and open source flight computer that includes an artificial horizon. It runs on your Android phone, old PDA, and many other devices.

XCSoar is a very nice free and open source flight computer that includes an artificial horizon. It runs on your Android phone, old PDA, and many other devices. http://xcsoar.org/ http://xcsoar.org/ https://play.google.com/store/apps/details?id=org.xcsoar https://play.google.com/store/apps/details?id=org.xcsoar It's designed for sailplane, hang glider and paraglider pilots, and is slowly disrupting the incumbents in this space. Source code is C++.