Development on Tremulous is nearing completion, but before we can call it 'finished' it needs to be tested more extensively. The primary aim of this testing is to balance the mod, which is particularly important for Tremulous since the each of the two teams in the game are different. Balance data is generated daily that illustrates where the current level of balance is with various numbers of players. We have plenty of data for small games, but very little for higher volume games.
Tremulous can be downloaded easily in one big zip file that is regenerated weekly. Note you only need the big zip file, the individual pk3 files are for keeping up to date if new files are uploaded before the main download is updated. If you decide to participate, it is a great help if you also idle in #tremulous on irc.quakenet.org. All games are organised in this channel and there are always people around who can help get Tremulous up and running (which isn't hard incidentally -- just unzip into your Quake 3 directory and go). Our test server is server.tremulous.net:27960. I highly recommend you set cl_allowdownload to 1 in the console so that any updates will be automatically installed.