YACE64 is a Commodore 64 Emulator.  Other emulators just try to give a realistic visual and sound experience - YACE64 tries to transform the old technic of the 80's into a modern design and using state of the art technology like 3D, stereoscopie and virtual reality.  Also it tries to unmystify the internal operation of a C64 and 1541 with detailed traces, disamssembler and visual VIC debugger.