Smalltalk programming language
Smalltalk is sometimes seen as one of the better attempts at a properly object oriented language, which compared favourably in syntax with C++ or Java, but did not go as low level as C++. It was always a little esoteric, and developed (and still has) what can only be described as a cult following. It never seems to have been taken seriously enough to be used for a business language.
From the outset it included a full GUI mouse driven system, and a rich framework which actually implemented much of the kernel and IDE environment in SmallTalk code. Any of this code could be rewritten, or overridden. This means it is fairly powerful and adaptable. It is also a little slow because of this though.
Developers interested in Smalltalk may find the languages Ruby or Python interesting.
Modern implementations include Squeak - which is available on Linux and other platforms.