Google SketchUp is a free 3D modeling program aimed at modern-day construction projects — adding an extension to your house, for example. But that’s not all it can do.
I downloaded SketchUp and played around with it for a bit, and it’s got some surprisingly robust tools built right in — like the ability to draw a 2D shape and then stretch it in any direction to create a 3D object, as well as view your creations from any angle (useful for tactical maps).
With a bit of time invested in it, creating simple structures looks like it would be pretty straightforward, from modern buildings to sci-fi ships, medieval castles and open areas like jousting fields or combat zones.
Graphics programs aren’t my forte (to say the least), but I can see some good potential in it for GMs. Update: And based on the comments so far, there’s a lot you can do with SketchUp for your game!
If you give SketchUp a shot, or if you’ve already tried it, tell us in the comments!