Project64 is a Nintendo 64 emulator which at first seemed to have popped up out of nowhere. I had some trouble trying it myself as my PC doesn't meet the steep system requirements of Project64. Yet from what I have seen, if you have the right PC, Project64 will probably work better for you than any other Nintendo 64 emulator.
The system requirements of Project64 are high. Don't expect games to run well or at all if your PC doesn't meet these requirements: