Hi guy's just discovered this project / site. But even so i will jump in with my input to this topic. Ideally i run Ubuntu Linux as my main Operating System, but i still have not found an adequate CAD program that i like (or runs on linux), so as of now i use Solidworks for my engineering projects on a windows machine and I am quite happy if Solidworks files are available. Having said that though i do hope STEP files will be routinely provided and open source cross-platform CAD software will continue to improve in the future.
I have tried but did not like fully:
FreeCAD (clunky interface but it can convert STL to mesh to STEP)
OpenSCAD (too mathy / programmers CAD, but useful in some situations)
123D Design (not open source and MAC and Windows only, and slightly numbed down)
Onshape (web based, but awful)
TinkerCAD (web-based but too numbed down)