GameMaker Server is a GameMaker extension which allows you to add online INIs, online achievements, online highscores or online multiplayer to your game, without having to host your own server.
There are 986 developers using GameMaker Server, and 4,761 accounts have been registered. GameMaker Server hosts 1,235 games, and 119,815 logins have been made on 33,737 different usernames.
To use GameMaker Server, you'll need a GameMaker Server account, and you'll need to register as a developer. Every game has to be registered as well, before any of the online functions can be used.