ASK: is there a github for 3d objects?

Not sure exactly what you're looking for. But is STL file viewing on GitHub relevant? https://github.com/blog/1465-stl-file-viewing

I know that 3ds (the company behind catia http://www.3ds.com/products/catia/welcome/) has an online platform where you can download and upload designs.

I can't find the name any more though.

What kind of 3d objects are you searching for exactly?

Here it is, I found it!

http://www.3dvia.com/search/

Why not just use GitHub? What format are your models in? GitHub supports STL viewing in browser. While STLs don't carry as much data as you may want, that may be a start.