Mark Overmars is known for creating the game development engine called "GameMaker". GameMaker is a popular game development tool that allows game designers to create 2D games without requiring extensive programming knowledge. It was first released in 1999 and has since been used to create a wide variety of games, including both indie titles and commercial games. Over the years, GameMaker has undergone many updates and improvements, and it continues to be a popular tool for game development today.