GM Version: GameMaker: Studio 1.4.x
Target Platform: Desktop
Links: Official Website, Video
The Hello Mario Engine is an open source Mario engine for GameMaker: Studio that is feature packed, and designed to be easy to expand upon with user friendliness as a priority. The engine is fully documented with thousands of code comments, and includes tons of different powerups, over a hundred different enemies, and much, much more!
After you start up GameMaker: Studio, you will see an import tab. Click on it, and import the HelloMarioEngine.gmz file included with the download. Read the included readme and manual for additional information.