The system used for the original Hi-Res Adventures: Mystery House, The Wizard and the Princess, Mission Asteroid, etc. Multiple sources online say they use a system you called Adventure Development Language (ADL) (example: this MobyGames page, this page on the ScummVM wiki), but I guess maybe that’s inaccurate and you used a different name for the engine internally?
So anyway, that’s what I’m currently trying to find out more about: the system behind the original Hi-Res Adventures from back when Sierra was still On-Line Systems. Do you know whether there’s any technical information on that engine, and the internal format of the game databases, available anywhere?
I definitely do plan to cover the AGI and SCI systems on my blog too a bit later down the line, but as you say there’s tons of information online about them—it’s the system behind the Hi-Res Adventures I’m having trouble finding anything out about.