C-Macs is a unique Cocoa application that pushes the boundaries by being written entirely in C, with no Nibs or Objective-C code. It is remarkably efficient, using minimal memory and featuring a red square drawn in Core Graphics. The author provides no license, warning users to proceed at their own risk and avoid using Objective-C in extensions. The app has some bugs, like not releasing allocated memory and relying on __attribute__((constructor)), but is built and tested on OS X Lion. It theoretically works on modern ObjC runtime-supported machines, but is not recommended for older OSes.
https://github.com/CodaFi/C-Macs