My brain gets stuck on music theory in odd ways, and unsurprisingly I can't find an app that addresses that exaaaaaact thing. So I keep building myself little websites, and I now have enough to put them all together for you in a box, in case this is exaaaaaactly what you were looking for.
I thought one way I'd improve my sight reading was by seeing the same note across multiple octaves on the staff. ↬ visit
Sight reading, one note at a time. ↬ visit
It turns out the alphabet is hard in a second language, and asking me "what comes after C" sends my brain in an infinite loop. ↬ visit
Get random strumming pattern. Strum it. Repeat. ↬ visit