Standing Ovation SRD - A simple high stakes system for solo games. I've done a couple of games in this, and will be creating a third for this. (I think We Will Not Go Quietly could do with some mods, tbh)
The Devil Jonah's Leviathan - Very cool game with a very cool bespoke system. You could always grab the mechanics, but I think the setting itself is crying out for expansion and adventures.
Amontillado - This is the first game I made on my own, without cribbing from a pre-existing SRD. I think it's a simple, elegant system for a quick two player game with escalating stakes and a nearly pre-determined ending.