Lightspark is one of the most promising open-source projects aiming to provide better Flash support on Linux and other operating systems. Lightspark aims to support the newer revisions of Adobe's specifications while also having fall-back support for using the open-source Gnash player for older versions of Flash. Among the recent advancements to Lightspark has been EGL/GLES2 support for Flash on ARM and an SDL-based audio back-end.
Lightspark 0.5.3 is the new version as the December release and it brings "robustness and portability fixes and a working Windows port."
The latest Lightspark release can be downloaded at Launchpad.net.