Recently I've stumbled upon yet another beta demo of
Powerslave, presumably released somewhere between the first public beta and the demo builds that are identical to the final release of the game. This demo (it's called "freeware" in the readme) still has the beta title screen, and a rolling introductory text not found in the other versions of the game. The two demo levels are practically identical to the first two levels of the full game, albeit there are minor differences. Some graphics and sounds are different as well.
Powerslave Freeware Part 1
Powerslave Freeware Part 2
Powerslave Freeware Part 3