"The editor for the Trine games gives users a first-hand look at the development process," Frozenbyte says in a press release. "Players can now do the same things to Trine or Trine 2 as the developers; they can edit existing maps to their liking, create entirely new ones from scratch, or even create a completely different game."
Both Trine and Trine 2 are free to play this weekend as part of Valve's biggest free weekend ever. Trine wasn't listed in the original free weekend announcement, so that's a nice surprise. Games in the deal are free through Sunday, October 19, at 1PM PT, and they're on sale through Monday, October 20 at 10AM PT.