Note Limiter has a single purpose -- to limit the number of MIDI notes that it allows to pass. It has control over voices (polyphony) and minimum time between note-on events.

Download the newest release or clone this repository, and drag the NoteLimiter.amxd device into a track in Ableton Live.
Max Voices dial to control polyphony (first note always wins). When the value of this dial changes, an "all notes off" message is sent to the MIDI output.Min Time dial to control how much time is required between note-on events.