i have one now, mostly working. i've been posting in the "General Q&A" area (to thundering silence
i wrote it in Processing, which i don't particularly like (but in fact i dislike writing graphical desktop programs to begin with, lol) so it will work on win, osx, *nix.
it does serial port-discovery, load/save file, edit cell, get stuff from the MJ. in a day or two i'll have it writing back tot he MJ (i've been testing indoors on a crap MJ simulator i cobbled up from an Uno). there's the usual various bugs but in a few days i intend on using it.
here's what it looks like. i ask you to squint, to overlook the mistakes, for now, lol. (the red error caused by unplugging the dongle). some spurious screen writes. i have some questions regarding data meanings (eg. version info). no matter, i will blunder along and make it work well enough for me (YMMV!)