Nintendulator started out as NinthStar NES, written by David "Akilla" De Regt. Written in C++, it was a reasonably accurate (and slow) NES emulator which used NESten 0.61's mapper DLLs. Numerous other systems were planned to be emulated within NinthStar (as well as complex debuggers for each of them), but somewhere along the line, the project was abandoned.
At that point, I took the existing NES sources and started improving them. First, the PPU was rewritten to be much more accurate than before, running cycle-by-cycle according to documentation that had been released at the time. After that, the CPU was rewritten to execute instructions more accurately. Then the APU was mostly completed, giving the emulator proper sound. Somewhere along the line, it was determined that the C++ usage in the code was very poorly done and was slowing the program down, so I converted it to plain C and named the program "Nintendulator".
The eventual goal of Nintendulator is to be *the* most accurate NES emulator, right down to the hardware quirks. In the meanwhile, it can certainly be used to test NES code with confidence that if it works properly in Nintendulator, it will probably work properly on the real hardware as well.