MusicTheory.net offers free online music theory lessons covering everything from basic note recognition to difficult chord inversions. Each activity on the site provides instant feedback. The exercises can be customized to test users on the notes and concepts they need to practice the most. Scroll to the bottom of the exercises page to find the customization options. MusicTheory.net also offers calculators and tools handy for composing music. And if you just need some staff paper, MusicTheory.netoffers sheet music that you can print.
Applications for Education
MusicTheory.net's lessons and practice activities offer a range of difficulty wide enough for the site to be used by brand new music students and older music students alike.