Urban Terror is a free multiplayer first person shooter, that (thanks to ioquake3) does not require Quake III Arena.

Packages are available for the following releases:
Ubuntu 16.10: 1:4.3.2-1~getdeb1
Ubuntu 13.10: 1:4.2.018-1~getdeb1
Ubuntu 16.04: 1:4.3.2-1~getdeb1
Ubuntu 14.04: 1:4.2.023-1~getdeb1
Ubuntu 17.04: 1:4.3.2-1~getdeb1
Ubuntu 12.04: 1:4.2.018-1~getdeb1
Ubuntu 14.10: 1:4.2.023-1~getdeb1
Ubuntu 12.10: 20100418-1~getdeb1
Ubuntu 15.10: 1:4.2.023-1~getdeb1
Ubuntu 15.04: 1:4.2.023-1~getdeb1
Ubuntu 13.04: 20100418-1~getdeb1

Package downloads per version:
Version 20100418: 77
Version 4.2.018: 820
Version 4.2.023: 3678
Version 4.3.2: 2102

Install the application manually with the following command:
sudo apt-get update && sudo apt-get install urbanterror

Uninstall the application with the following command:
sudo apt-get remove urbanterror