Guitarou

One of my favorite old songs to loop and perform development to. This version was taken from the "additional files" of a Duke Nukem 3D CD-ROM, then properly decoded, dual-channel, stereo, and amazing. So far better than most other versions you'll find. It's just... epic.
Reference thanks to ‪@JukkaMTAho‬ :
“Guitarous” was originally composed on the Commodore Amiga using the ProTracker music sequencing software. It was released as part of some Grace SF demoscene production. As usual for demoscene music, the song was then “ripped” (extracted from the demo) and started circulating as a bare ProTracker module file in dial-up bulletin board systems and the like. Someone called Alexander Stock then apparently included it as a sample tune with his MOD2MIDI tool (written for MS-DOS), which may further have helped it getting some exposure across platform boundaries.