Self is the language that invented prototypical inheritance and the Morphic UI framework, one of which (morphic) is now used in pretty much all modern Smalltalks, and the other of which (prototypical inheritance) got picked up by a little language called Javascript, which you may have heard of. In addition, Self provides provisions for multiuser networked UI, kind of like Google Docs does.

Given, it's not exactly usable for modern projects, but it's worth studying.