yeah, seemed like for a while there were quite a few DIY arduinomes out there.
the arduinome source code is still up:
[ https://sourceforge.net/projects/arduinome/files/Arduinome/ ]
[ed: woops, fixed the link]
tbh, it’s… well it’s not the prettiest thing i’ve ever seen. derived from original 40h firmware i think.
(you know all the official monome device sources are online right? https://github.com/monome/mk )
the official firmware itself is done in a very clean but very direct, low-level style squarely targeting 8-bit AVRs.
i have long thought that a nice modular, platform-agnostic implementation of the device side serial protocol would be a cool thing to do. but have never got around to it