Skalenmeister is a MIDI effect that forces incoming notes to a given scale and key. Additionally it can generate chords from single notes (with basic strumming effect). The fourth note of the 7th and sus type chord can be changed e.g. to generate add9 or something else. The strum delay of the 4 note chord can be adjusted (up/down) and the root key for the scale can be determined by the incoming note for the chord generation or on a second MIDI channel.
Also, included is Polymeister, a force2scale plugin for polyphonic input (without chord generator).