I've been following the Gnash project for quite a while now. It is a free software implementation of Adobe Flash, both a standalone player and a browser plugin. Gnash implement support for the AVM1 format (and not the newer AVM2 format - see Lightspark for that one), allowing several flash based sites to work. Thanks to the friendly developers at Youtube, it also work with Youtube videos, because the Javascript code at Youtube detect Gnash and serve a AVM1 player to those users. :) Would be great if someone found time to implement AVM2 support, but it has not happened yet. If you install both Lightspark and Gnash, Lightspark will invoke Gnash if it find a AVM1 flash file, so you can get both handled as free software. Unfortunately, Lightspark so far only implement a small subset of AVM2, and many sites do not work yet.
A few months ago, I started looking at Coverity, the static source checker used to find heaps and heaps of bugs in free software (thanks to the donation of a scanning service to free software projects by the company developing this non-free code checker), and Gnash was one of the projects I decided to check out. Coverity is able to find lock errors, memory errors, dead code and more. A few days ago they even extended it to also be able to find the heartbleed bug in OpenSSL. There are heaps of checks being done on the instrumented code, and the amount of bogus warnings is quite low compared to the other static code checkers I have tested over the years.
Since a few weeks ago, I've been working with the other Gnash developers squashing bugs discovered by Coverity. I was quite happy today when I checked the current status and saw that of the 777 issues detected so far, 374 are marked as fixed. This make me confident that the next Gnash release will be more stable and more dependable than the previous one. Most of the reported issues were and are in the test suite, but it also found a few in the rest of the code.
If you want to help out, you find us on the gnash-dev mailing list and on the #gnash channel on irc.freenode.net IRC server.