Selva3D is described as 'Transform images into 3D models online' and is an website in the Photos & Graphics category. There are three alternatives to Selva3D, not only websites but also apps for Self-Hosted solutions, Windows, iPad and Mac. The best alternative is Archipelis 3D. It's not free, so if you're looking for a free alternative, you could try Smoothie-3D or Monster Mash.
Monster Mash is a new sketch-based modeling and animation tool that allows you to quickly sketch a character, inflate it into 3D, and promptly animate it. You can perform all interactions in the sketching plane. No 3D manipulation is required.