Fever_Discordia: Forgotten Realms Unlimited Adventures
Yep, that's it. It's basically SSI's predecessor of the Neverwinter Nights idea. A game to create your own adventures with, in the style of their Goldbox games like "Pool of Radiance" etc. (hence the similarity to Buck Rogers and Krynn). It was only meant to create fantasy D&D adventures with, but like NWN it's got its own creative (and still active!) modding community which has greatly enhanced its possibilities over the years.
The first screenshot was an example of a modded ('hacked') module set in a custom superhero universe, "SuperDead" by hans. The last screenshot is from "Heirs to Skull Crag", the campaign that shipped with the editor.
This definitely belongs on GOG, if only for the huge amount of excellent fan-made modules available for it. Everyone who showed an interest in this game should immediately go to the wishlist and vote for it! :D
Your turn, Fever_Discordia!