On source forgehome page, scroll down to software categories, click on multimedia, then look over on the right and you'll see a list of project topics. click on multimedia graphics,  then you'll see links for 3d modeling and 3D rendering. Having just looked I can see 736 listings for modeling and 1515 for rendering. Most of those will be useless for what you want, but many of them could be very useful.  Most source forge softwares are free.

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