For the past year, Alessandro Pignotti has been writing a FLOSS Flash player entirely from Adobe's released SWF documentation (read: no reverse engineering) and now he has felt it has reached a beta status. This Flash player is called Lightspark and it currently supports OpenGL-based rendering, a mostly complete implementation of ActionScript 3.0, a Mozilla-compatible plug-in, and performance profiling/debugging features.
OpenGL rendering is being used in Lightspark over X-Video as it makes it possible then to support any of the Flash overlay/transformation effects. The ActionScript 3.0 support is implemented by an interpreter and JIT engine that utilize LLVM, the Low-Level Virtual Machine.
Details on the Lightspark status and Launchpad PPA information can be found within Alessandro's blog post.