alt Hacker NewsWeb servers, message brokers, physics engines, anti cheat, fraud detection, flood mitigation, ranking systems, chat moderation, match making systems. There are thousands of possible components which may have been licensed in any given game server system. In some cases the entire game engine runs on the server.
I guess what surprises me here is how much of this is 3p code that couldn't possibly be distributed. Like why would you not be using an open source web server, or widely available message broker? Things like chat moderation/match making/anti cheat/etc seem like add on services that would be implemented per game (well, maybe not match making) and aren't relevant to the problem that the "stop killing games" people are trying to solve.