For those that don’t know GameSpy was responsible for a lot of online multiplayer services from ~2000 to 2013 when they were shutdown.

Some games were updated to accommodate for this and fans created game-specific solutions for certain titles such as SWAT 4 and Crysis and more universal solutions like OpenSpy.

The PCGamingWiki page is great if you want to see if your favorite games from ten to twenty years ago still have working multiplayer.