Here are two Let's Plays (text) devoted to SSI's classic DOS D&D "Gold Box" construction set program Unlimited Adventures, one of the most revered user-level RPG creator programs and now available on GoG.
Let's Play UA, an ENWorld forum post.
Another text Let's Play, on RPG Codex.
UA modules are not easy to get running, but for those interested....
"I am after all proposing that I showcase 30 year old modules (Castle Amber, Temple of Elemental Evil, etc), via a 25 year old RPG system (2nd edition AD&D), using a 20 year old video game (SSI's Forgotten Realms Unlimited Adventures)." — UA Let's Play on ENWorld.
Modules & Sites
A collection of modules based off of classic pen-and-paper D&D modules. The website The Realm suggests an order of play and sets them in a campaign world.
The UA File Archive, with an archive of UA newsletters — and the newsletter seems to still be active!
UA fan site (Wayback Machine)
Art for UA adventures
Video Demonstration
YouTube video of the editor.
Video Review Part 1 - Part 2
Utilities
Gold Box Explorer is a program for decrypting the assets from Gold Box games.
UA Shell is a program for running UA adventures hacked to allow for more options and to fix bugs. What is UA Shell? (Wayback) UA Shell can be obtained here, but you're on your own for using it.
Dungeon Craft
Dungeon Craft is an open source RPG engine inspired by Unlimited Adventures. After a long development period, it graduated to version 1.0 in October of last year. It's a bit clunky to set up though, and I cannot vouch for how it runs. It claims to be able to make standalone games.
Dungeon Craft project site.
Dungeon Craft adventures.
Dungeon Craft fansite. (Last updated 2007)
Unlimited Adventures can be legally obtained from GoG's Forgotten Realms Archives Collection Volume 2.