If you've spent any time whatsoever in SketchUp, there's a better-than-average chance you'll have a ball within Autodesk 123D. The new Windows-based program -- which quietly slid into beta a couple of weeks ago -- is a gratis, stripped-down version of Autodesk's famed Inventor application, but it still offers a plethora of design tools for something that's being given away free of charge. We're told that just the basics are here, and sadly, it's not open source; that said, it does have an option for exporting to STL, and you will find support for assemblies and constraints. Eager to toss something else in your 3D
