Attached Link: http://www.curvy3d.com/

One major difference: Silo is a polygonal modeller, like Wings. You push and pull polygons and edges, bevel or extrude them and so on. Rhino is a NURBS modeller. It means that basically everything starts with curves which then create surfaces. You can do extrusions, bevels and fillets, but everythign can be done with curves, too. As to the abilities of both, it depends on the author. The only one that I know with Silo is Kemal (and bobtronic over in Cinema gallery, but he has just one pic, AFAIR). Kemal does wonderful stuff with Silo. Rhino users appear to be technically oriented (me included :-)) and you can see cars and planes and stuff, but you also have Teyon who's wonderful with weird creatures and Xurge who models all of his Poser clothes in Rhino. OTOH, Silo costs $109, while Rhino is 895 euros (for you in Scotland. IINW). For the Americans, it's $895. Modo also costs quite a lot, $895, and it's something like Wings/Silo, cause it's a polygonal modeller. Other modellers would include Cinema, which is a full blown app for 499 pounds/ 499 euros (great speedy renderer and materials, too) and which has both polygonal and NURBS-like modelling. See Kromekat's, Cartesius's or 3D Explorer's stuff for models done in Cinema. I haven't tried Curvy 3D (see the link), but it has a painting approach to modelling and costs just $84, as opposed to ZBrush 2, which uses a similar approach, wonderful for organics, but costs $529 for the boxed version. IIRC, Zhann was a beta-tester for Curvy 3D and you should ask her about it.

-- erlik