Improvising to non-modal chord progressions such as those found in jazz necessitates switching between the different scales implied by each chord. This work attempted to simplify improvisation by delegating the process of switching scales to a computer. An open-source software MIDI remapper called ChordEase was developed that dynamically alters the pitch of notes, in order to fit them to the chord scales of a predetermined song. ChordEase modifies the behavior of ordinary MIDI instruments, giving them new interfaces that permit non-modal music to be approached as if it were modal. Multiple instruments can be remapped simultaneously, using a variety of mapping functions, each optimized for a particular musical role. Harmonization and orchestration can also be automated. By facilitating the selection of scale tones, ChordEase enables performers to focus on other aspects of improvisation, and thus creates new possibilities for musical expression.