There are none I know of, even for jaikbroken iPhones(but I'm not very up to date there)
I don't know if Apple forbids them through the apps store, how ever I do know one app "Sketches" lets you browse the web, then draw on the web page you stop at. I don't know if this builds upon Safari, or if its all on its own. I do know it looks a good deal different from Safari, but they could have just skinned it.
Edit- NVM, Google search and Jeremy1026 were right, its not allowed. At least according to the how Mozilla is reading it, it isn't quite as clear as "No web browsers other then Safari". I'd guess "sketches" builds upon Safari then.