Yeah it’s part of the new html5.
Sketchfab is free although your models are public if you want them private then you have to pay. Also it doesn’t import .3dm so you have to translate them to something .obj. There are plug-ins for other programs like C4D that will bundle up and import all the textures straight in sketchfab, but currently there isn’t one for Rhino. There are some other cool features like being able to embed the files into websites…ect
Beer Bottle (click to view in 3D)
Grabcad Workbench is pretty cool as well. You get 2 projects for free, with some other limitations. This you have to invite other to join the projects. The nice thing about workbench is you can see the assembly structure and do exploded views right on the fly, along with some rudimentary markups and measuring.
Kenesto seems to be set up as a full collaboration community for everything not just 3D models. The community is free but they also have business edition which you have to pay for.
Gteam is made by Gehry Tech. and is geared towards the AEC community. Although it allows you to upload other project related stuff as well. You have to pay for this service although it’s got some cool features like clash detection. I was a beta test but as soon as went live we didn’t pay for it.