What is Nestopia?
Nestopia is a NES emulator that was written in C++ and it is perfect for games requiring precise timing since it is very cycle-accurate. With support for an incredible amount of mappers. It also supports NSFs, the famicom disk system, save states, IPS patching, battery-saved ram, NES movie files, and many VS-Unisystem games. Finally, it emulates four non-standard controllers (including the Power Pad).
The project is no longer developed. Last version, 1.40, released in June 2008, can be still downloaded from the official website.