Solo Noir
Solo Roleplaying Secrets & Lies
I am a huge fan of games that I can jump straight into without having to digest 500 pages of rules and options before making a 1st level character. Secrets & Lies by Daniel Bayn is just 33 pages, and PWYW. The book gives you three different settings, but it is the classic noir detective that spoke to me.
The standout design feature is how Secrets & Lies is built on presumed success. Many games have characters that will frequently fail at even the most central of tasks. Thieves that cannot reliably pick locks and fighters that miss as often they hit with their swords. Secrets & Lies is not like that. You describe what you do, and if success is important you make down a 'hit' against your vitals and carry on. Then when you reach a crucial moment, that is when you go to the dice and all those hits can come back to bite you.
This mechanic means that you can do whatever defines your character, you are competent and capable, but there is always a cost to pay in the end.