These entries are about playing against other people. The Quake family, Return to Castle Wolfenstein, Urban Terror and the two Half-Life and Counter-Strike builds all connect to live servers, and several of them are the same family of projects hosted under different addresses. Latency matters more here than anywhere else in the library, so expect the experience to depend on your connection and on how far the server is from you. CS Surf is the outlier: it drops the shooting in favour of movement, and it is one of the quickest entries to get into.