Donkey Kong
There are all different kinds of arcade romhacks out there. You have: One of the most impressive hacks I have seen yet, though, is the new version of Donkey Kong available from Jeff's ROMHACK page. This guy disassembled the ROMS in Donkey Kong and examined thousands of lines of code. After months of work, he was able to: You used to think the elevator level was hard when you first played Donkey Kong? You ain't seen nothin' 'til you play this new level.

DK Extra Animated This level takes a keen skill in jumping.

The extra level actually feels like it belonged in the original game =D

DK Extra DK Extra DK Extra DK Extra DK Extra

LINKS

Jeff's ROMHACK
Customize Your Arcade Game

Tiny MAME Build for Donkey Kong
Source code included. Don't forget the samples =D