icculus.org has released a dedicated GNU/Linux server for Call of Duty 4: Modern Warfare, first person shooter sequel developed by Infinity Ward. You'll need to copy the data files from a Windows install. Punkbuster works, but you'll need to run its installer separately (instructions on how to do this from the commandline on your remote server are in the README).

Call of Duty 4: Modern Warfare Linux Server (3.61MB)