Still haven't seen an idea as good as the Bushi in Adventures in Rokugan.
Having a per-turn generated 1d4 points that you can stack (to a cap) and spend on abilities is super fun to play. Being able to replace attacks and use them as reactions and bonus actions gives a fighter a chance to play simple (favoring just 1-2 techs) or get really diverse and go all out trying things.
The Bushi even works in core 5E, and is pretty much balanced along 5E class lines. If 5E ever just adopted the idea, man, like, even children can do it. No dice to keep track of. Per turn. Mmmm heat.