Flashnote Derby is a fun app that has many options for learning notes. You can drill by note name, piano keyboard, or microphone input. It is cross-platform for iPad, Android, and even Kindle (the Kindle version does not have microphone input)The range of the notes is great and the flexibility to choose the exact notes you want to drill is wonderful. There are some downsides - there are no options for drilling flats or sharps, and the microphone input will only work for instruments in the key of C (and also not guitar, as the guitar notes sound 1 octave lower than written). But for getting students started on the basics of note reading, it has been an indispensable app for me!