The Unvanquished open-source game made a heck of a lot of progress in 2013, which they've recapped the progress of their first person shooter game on their web-site.
Throughout 2013 there's been monthly alpha releases by Unvanquished and these updates have been heavy with new features. Details in full can be found via their web-site while some of the big items include many advancements to their OpenGL 3 renderer, new game models and other in-game assets, game-play improvements, visual improvements, multi-threading / SMP suport, SDL 2.0 support, and the first bits of their engine upgrade branch were merged.
The engine upgrade work is rewriting their ioquake3 engine from the former Tremulous game into a C++11 code-base
and supporting many other modern game engine features compared to id Software's Quake III engine. The new Daemon Engine will also feature Google Native Client support.
Development of Unvanquished is picking up as are visits to their web-site. More details on the improvements made to Unvanquished this year can be found via their 2013 year-in-review
and the many Unvanquished articles on Phoronix
Unvanquished along with Xonotic continue to be the two leading open-source first person shooter games that I feel are worth paying attention to by open-source gamers for delivering a more polished experience than the many other open-source game projects out there with low-quality assets and lack of driving original developments into the engine.