What kind of supplements can you take legally that help you focus?

Of course I know the basic ones like caffeine, taurine, ginseng, and omega-3, but I'm looking for something more effective. I would say caffeine is probably the best stimulant that you can get legally, but it just doesn't cut it anymore. I don't want to resort to using adderall/vyvanse (which would be obtained illegally), so does anyone know of anything effective?