I was searching on Youtube for various stuff about 3d game development and I found this:
Sandbox is a game design tool based on the Cube 2 engine that allows users to quickly and easily create and edit their own worlds in game, even cooperatively. It is free, open source, and easy to use for Kids and Adults.
It's not like Gamemaker but it looks interesting and easy to learn so I will give it a try.
You can download the program for FREE from the official site here.
source: http://www.sandboxgamemaker.com
EDIT: Only for kids. . .