I’m currently editing, doing some minimal design, and finishing the gods-damned bestiary in my Old-School game system, Stone Halls & Serpent Men.
The elevator pitch is: A small role-playing game for running Old-School adventures.
The keys there are small: About 20 pages, with everything. I’ve made smaller, of course, but not that can run a long-term campaign of old modules.
Old-School: The Old-School Renaissance for me was entirely satisfied by Supplement V: Carcosa, Swords & Wizardry, and Lamentations of the Flame Princess. But Carcosa’s a super deviant SF/Lovecraft setting, and the latter two are somewhat long, discursive, full of optional rules or details you don’t need if you’re creative enough to Referee in the first place.
New, less trashy, more flexible game designs, with no page of OGL legalese gibberish, don’t accomplish the goal of rolling characters in 10 minutes and crawling, desperate and dehydrated, into B4 The Lost City.
In Jeff Rients’ threefold model, SH&SM is Retro, maybe Retro-Stupid. I’ve done one thing I think is really clever, and the rest is a functional listing of the absolute minimal rules needed to play.