Download GNU Gnash
Gnash is being actively developed at the moment. Therefore, although many features work, not all movies play successfully. The latest beta release of Gnash has been made at version 0.8.10 in mid Feb, 2012.
Win32 users can now download an executable based on the 0.8.2 release, which is now seriously out of date, and won't work with YouTube.
Git Access to Sources
The latest Gnash sources are also available via anonymous access. You will need the Git program (usually contained in a package called "git").
git clone git://git.sv.gnu.org/gnash.git
For more detailed information on git usage at gnu.org, read git usage at gnu.org
If you require a source tarball, you can get the latest version from a directory of daily snapshots on the web.