A launcher/downloader/manager for games from GOG.com and other services.
In order to get this to run you need a recent XULRunner version from ftp://ftp.mozilla.org/pub/xulrunner/nightly/latest-mozilla-central/
Put the XULRunner directory (not its content) from that archive into your repository. Don't worry, it will not be synced. Take the xulrunner-stub.exe and copy it into your repository directory. Rename it to GamesDesktop.exe to keep it from getting synced.
For now, the code is Windows-only, although there are discussions about a cross-platform toolbox.
All discussion happens (for now) over at this thread at the GOG forums: http://www.gog.com/forum/general/gamesdesktop_a_launcher_for_gog_prealpha_help_needed/page1