I recently set myself the goal of learning piano. I'm kinda familiar with music theory but my self-discipline is terrible, and I needed someone to keep track of the songs and scales I'm practicing, remember how I'm doing and tell me what to practice next.
This app does that. It will keep track of your progress so you don't have to, and it knows just enough music theory to know what you should practice next.
It uses a simple rating system (red, amber, and green) so you get an immediate idea of what's going well (and not so well), and even has a handy practice timer to keep you honest.