As Michael suggested, you can try Archipelis and Teddy which are both mesh metaball modelers, but using curves to drive the shape. You can also try Shapeshop which is like Teddy and Archipelis and has more advanced interface than both. I've tried all a while back, and they are fun to play with. But the mesh produced from meta modelers is typically undesirable (in othewords, it's about as neatly constructed as a plate of spaghetti)... Somehow i think what you are wanting is more like the Rhino plugin called RhinoArt. But i don't know of any stand-alone application of the same function...

jonah