Shooter Nexuiz is now host to Duel Mode on PC, courtesy of some DLC. If you're the competitive type with a love for classic competitive Quake matches and the like, this should be right up your alley.
Duel Mode features 1v1 matches on three new maps exclusively designed for this purpose. It'll run you a reasonable five dollars normally, though temporarily you can grab it for a little over three dollars.
Hit the source if you're interested.
As mentioned previously, Nexuiz had mixed reception on console, but has had seen quite a lot of enhancements on PC, so could be well worth the look now.