I don't think they're too many free programs to do that... I used Luxion Keyshot 2 for these renders
Rendering time? About 7 minutes each one, at 1800x1050
"It's not free", but I think the trial allows you one month. I also was part of the beta tester members for Bunkspeed Shot, which has been released recently, I'll try the final version shortly
![Nod](/static/smilies/nod.gif)
There are many others, aswell as plugins for your 3D software like 3DSMax, Rhinoceros, Maya... but none of the ones I know are
legally free...