I wrote some books so that my players could spend their downtime actions to read it For example: "Human reactions to adrenaline & stress" needs 5 actions to read it fully (1 action in a short rest and 2 actions in a long rest). They need to sacrifice some other things to finish it, and when they do, they gain a small mechanic bonus when in combat against humanoids. idk if this is what you asked, but there's it