EEXIST began as an experiment to create a "zero-bit computer" (ZBC), i.e. one whose instruction set had a length of zero bits. Zero bits allows for a single opcode; thus, a ZBC contains only a single instruction. Such a machine has been defined, emulated and used to implement simple algorithms. You can read the initial whitepaper on this here. Source code for the emulator, as well as some sample programs, can be found here.