A kit for reading and writing Roland Expansion Boards, for adding extra sounds to some synths. You can write images of Roland's (expensive) existing boards, or create new boards with your own samples.
https://www.sector101.co.uk/sr-jv-romulator.html
Here's what I did to write boards in Arch Linux.
I had to do a restart for the board to get connected properly. In the end it is at /dev/ttyACM0. You can check with dmesg after you plug it in.
On the website there's a guide linked that uses Minicom, but I haven't been able to get that to send files. I suspect it's something to do with the script, maybe the progress bar, so I'll try again next time. In the mean time I had success with Cutecom, after also trying GTKTerm and PuTTY.
Ultimately I found the Mac guide more useful. The key settings you need to do are:
Once you're connected to the Romulator the process to write a board is:
cd to get board info.er all to wipe the board.prg [size] to allocate the correct size for your board image. The official boars are the full 8MB, so you'd enter prg 8192.