Emulate an Intel 8086 CPU
I know that there already is a code golf for this, but that one didn't require much. This one, however, is for masochists only! >:) OK, you need to emulate an entire 8086, every single opcode. Not every flag needs to be computed, but every single documented opcode needs to be implemented.
However, that's just the beginning. I STRONGLY encourage you to support more than just this. NEC V20? Why not? Soviet clones? Don't mind if I do.
For some help, opcodes 0x60 - 0x6F are just aliases for opcodes 0x70 - 0x7F on the 8086 and 8088 ONLY. If you ask the guy who runs reenigne.org, he'll say the same thing, simply because it's been proven by hardware tests, on an IBM XT.
Anyways, for bonus points, emulate an entire V20, 286, or 386, no facets left unemulated.