iReal Pro is such a great app! It’s been a while since I’ve touted it, so here I go again.
Quick transpositions (I often switch between guitar and trumpet until a tune is memorized), easily print and send right from your phone or iPad. Backing tracks that aren’t too cheesy to practice with, and you can get thousands of charts for free from the online forums. It’s an amazing app. You should get it. Not just for jazz players, either.
Tutorial videos here.