I googled and found a couple of open source programs. Didn't read enough about it to know for sure, but maybe someone could make a plug-in to export to one of them. Blender apparently has something started for Freestyle... So you could just export from Wings3D and use Blender.... beating Ran13 to the punch... 
Freestyle Freestyle Homepage
Ink9000 Ink9000 Homepage
oort

Freestyle Freestyle Homepage
Ink9000 Ink9000 Homepage
oort