It's probably not got the entertainment factor of Guitar Hero, but I'm working on an Android app that connects via Bluetooth/USB MIDI and teaches you sight reading. It starts with individual notes, then progresses to intervals, triads and more complex chords. All of these are exercise based, so you can pick and choose areas to focus on.

The notes are all rendered according to conventional music notation standards as per Elaine Gould's book "Behind Bars". Writing this code was not straightforward, but worth the effort as it's very flexible.

Progress is tracked intelligently, i.e. accuracy and response times are recorded per note, and exercises can be directed towards improving weak spots. This was all borne out of a frustration I had with how long it takes, and how much material is needed to make progress with sight reading skills.

I'm hoping to release it soon (next few months - it's mostly finished), but slightly concerned it's too niche. I guess it will mostly appeal to serious but beginner/intermediate pianists who want to put in the hard yards to develop sight reading abilities to an advanced level.