At some point, most inquisitive guitarists confront the intricacies of modes. Ninebuzz’s Modal Buddy is an iOS app that breaks down modal theory and lets you practice modes in context. The beautifully designed app has two main sections: learn and practice. The learn section walks you through six chapters of examples that explain how modes are created and why they work with specific chords. Some of the Q&A information is questionable (like the suggestion that a Mixolydian scale works well over a major 7th chord), but most of the info is pretty solid.
Once you get the concepts under your fingers, the practice section provides various backing tracks for working out modal ideas. Each example shows the five main fingerings—based on octave shapes—and offers a vamp (in the relative key of G) to solo over. Unfortunately, the vamps are only available in one key, and most of the theoretical info is available for free online. (Plus, at five bucks, Modal Buddy does far less than other comparably priced apps.) Modal Buddy isn’t something you’d want to break out on a gig, but it’s a well-designed practice tool that may help guitarists get past important theoretical hurdles.