Hallfiry was able to obtain a copy of the early demo CD of Daggerfall, which has the female Spellsword. Details and download links are here. And here are the photos of the CD and its cover.

I'm so thankful for this thread! I'm working on a YouTube playlist of my favorite exclusive content demos.

Jagged Alliance 2 has the "Demoville" map (with three levels, one of which is hidden) that is unique. The non-battle area of the ground level is slightly similar to I06 Estoni. The demo also has some exclusive voice acting.



https://archive.org/details/JaggedAlliance2_1020

Correction: StarCraft the demo has 4 levels + 1 tutorial level, not 5 levels + 1 tutorial level:


Fallout 3 Van Buren has a demo. It was never made (or at least never released). Not sure this counts.