Game Engine: BYOND (Build Your Own Dream Network): Dream Maker
Description: A massive multiplayer online client/game maker for free of charge. Many games have been made through this and are published on the Byond Hub to play at any time. It supports Windows graphically only. You can host it on MAC or Linux however. It does not support 3D but supports 2D and has a built in map engine to assist you in creating your game. A new feature is coming out for making isometric creating easier, if you're interested in designing in it. You may choose to charge (though not common) to play for your game through memberships and such if you wish, or create it free to play. No royalty fees or any kind. The game you make is YOURS.
Platforms: Windows (fully supported), MAC & Linux (only can host)
Genre: 2D massive multiplayer online games: platformers, RPGs, adventure, etc.