Objective-C was invented by Brad Cox in 1984 as a superset of C with Smalltalk-like extensions. The merging of these two disparate languages worked surprisingly well, and Objective-C remains the most dynamic of the C-based OO languages.
Objective-C was the flagship development language of the former NeXT Computer, Inc. Their UNIX-derived operating system, NeXTstep, was powered by thousands of high-quality Objective-C applications. In 1997, NeXT was acquired by Apple Computer, Inc. where Objective-C lives on as one of the available development languages in the MacOS X development environment. However, in recent years Apple has played up Java while downplaying Objective-C.
Outside of Apple, you can find Objective-C through open-source projects such as GNU's gcc and the Portable Object Compiler (poc), but an examination of comp.lang.objective-c shows little activity for the Objective-C community in general.