Where I made my name in solo play was by having rules that were tightly focused on each specific game system. You didn’t need to break out of the headspace of the game just to use a generic oracle.
What I was doing is looking at my collection of games and picking the ones that I really wanted to play but there was no way my regular group would play them.
It feels like I fell out of that.
I recently picked up For Coin & Blood (Gallant Knight Games) and I really want to play it. It has elements of those OSR/0D&D rules, but it also have elements of Fantasy AGE/AGE System. For example, AC has gone, you roll to hit against the characters defence attribute. Armour now has a reduction/soak value.
FC&B also has a few OSR style classes, but your profession is completely separate from your class. Your class gives you core class abilities like proficiency with weapons and armour or spell casting. Your profession gives you the skills that a professional would have. This is very much like choosing your focuses on the AGE system.
I can also see hints of Savage Worlds in the rules, but they feel more like an idea that was early in the design process but got side lined during different revisions until there are just vestigial remains.
It has long been my intention to make some dedicated rules for Old School Essentials. I would like to try out some of those ideas in FC&B first and see how they work before taking on OSE, which is a much more popular game.
I think I can create a full set of solo tools for FC&B in a week. This is going to be my next project.