NEXUIZ and XONOTIC

Apparently pronounced like "nexus", Nexuiz is a fast-paced arena first-person shootout quite reminiscent of Quake and Unreal Tournament. Though I've only just recently discovered the game myself, I've learned that it has been around for a few years now, originally developed as a mod for Quake and later being released on the old X-Box as a full game. These days, however, the game has become an open-source project which of course means that it's TOTALLY FREE. (With that statement I should clarify that I'm talking about what is now referred to as "Classic Nexuiz" which could easily be confused with a newer version of the game.) Rather than bore you with a TL;DR description here, I'll instead embed a YouTube video so you can see the actual gameplay for yourself:

To make a potentially long story short, at some point the developers of the open-source Nexuiz for whatever reasons split into two separate teams, one group continuing to work on improving Nexuiz while the other group went on to further develop their own very similar but new version of the game called Xonotic. (Fortunately, like it's parent game, Xonotic is also TOTALLY FREE.) Again, rather than bore you with a wall of text comparing the two games, I'll embed another gameplay video for your viewing pleasure:

Though both games are obviously designed for multiplayer action, antisocial gamers like myself might be pleased to know that each game has a single-player mode as well. In each case, you can choose between playing through the maps in a predefined succession or maps that are randomly selected, all the while fighting against opponent "bots" that are trying to toast you as you attempt to achieve your goal of either surviving for 5 minutes or scoring 20 points.

In short, if you (and your friends) are into "deathmatch" games like this you might want to check out Nexuiz and Xonotic. Since they're both free there's really nothing to lose by giving them a try. Did I mention that both games are totally free? I love free games...