For those who mis-read that other submission (AnduinOS) and were hoping for an Arduino operating system.

Looks like an absolute riot (heh).

Glancing at the sample code, the API looks quite pretty. It fits nicely with the "imperative-ish C++" idioms throughout most of the Arduino SDK. The reliance on try/catch statements is peculiar. If I'm doing something that demands a multitasking kernel, Arduino is never the first thing I'm going to reach for. Looks pretty nicely done, though.

Seems like an alternative to freeRTOS / RIOT.

Last commit was 8 years ago? Does anyone use it?

Sadly that is 9 years ago.