Here's this silly little thing:
https://stash.reaper.fm/23467/octave%20squisher
It only works on one MIDI channel at a time (everything else passes through), takes any MIDI note input and transposes it up or down by octaves so that it fits in the range specified by the sliders. Not much to it, and there are probably other things out there which would do it, but it is a simple solution to an issue I have fairly regularly.
Seems to work pretty well given very basic preliminary testing. I haven't really heard the results, or tried to hard to break it, but the results look good. Any comments, concerns, or suggestions are appreciated.