Lecturing and Teaching at Universities

As some of you know I am an active teacher at two universities. One course is Game Design at the Media Design Hochschule in Düsseldorf (also active in Munich and Berlin), the other one is the famous Filmacademie in Ludwigsburg (even earned OScars for their films).

At the first I am looking for an easy to use level design tool with a game attached already. They need to learn the tool pretty fast and be able to design a complete, playable level within 1-5 weeks. Any recomodations? This can be an online game, single player game (any genre) and needs to be freely available.

Please leave comments about recomodations.