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 1,108 developers using GameMaker Server, and 5,519 accounts have been registered. GameMaker Server hosts 1,404 games, and 142,101 logins have been made on 39,052 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.