What are some alternatives?
When comparing Counter-Strike and Quake, you can also consider the following products
Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
Battlefield - The latest news and updates for all things Battlefield, the EA and DICE video game franchise.
Doom - Doom is a science fiction horror-themed first-person shooter video game in which players assume the...
AssaultCube - AssaultCube is a FREE multiplayer first-person shooter game. Taking place in realistic environments, with fast, arcade gameplay, it's addictive and fun!
Unreal Tournament - Unreal is a series of first-person shooter video games developed by Epic Games.
Call of Duty - Call of Duty is a first-person and third-person shooter series by Infinity Ward.