HDNes is a Nintendo Entertainment System emulator that enables one to "display custom true colour tiles at up to 4x resolution". The emulator includes a graphics pack editor for creation and editing of these tiles. In Layman's terms one can play NES games at higher color depth and resolution.
HDNes requires an OpenGL 3.3 or higher capable graphics card / chip set. This should run on any fairly modern PC. Those with netbooks and older laptops will probably be out of luck - like me :)
Supported mappers are limited to 000-004, 016, 153, and 159.