GameSpy Technology has announced that effective May 31, they will cease providing hosting services for all games that still use their technology. The service has existed ever since the Quake days, and has provided things like multiplayer matchmaking, leaderboards, and the like across PC, consoles, and mobile.
A ton of titles are going to be affected by this closer. Some games over the years have phased out the service, but there are potentially hundreds that may lose the ability to play online. Reddit has pulled together a list of just some of the games that this will hit, including Halo, Arma III, Unreal Tournament, and much more.