Currently working on moving the ICS calendar parsing part from a python script down to the microcontroller itself, then I can release.
I'm running on an esp32, with platform.io, and esp-sdk + Arduino. Overall project: https://github.com/russor/ClockThing
iCal library: https://github.com/russor/uICAL (if I had know how much work I'd need to do to make this library work for me... I might have left it with my hacky solution of processing on my own server in perl in a cron... But I had too many messups with that)
FWIW, Google Calendar recently stopped including real Timezone information in the calendar urls for newly created calendars. I ended up doing something gross to manage that (got a dump of all the tzurl 'outlook' calendar files, and load that before loading the user calendar; it's sketchy, but it works)
I'm also on esp32, and have been wanting to write more using the native esp-idf tooling. I'm comfortable with Arduino but now that I'm getting into things like sleep modes and low-level IO, my code is becoming a patchwork of Arduino pinMode and ESP-IDF gpio_hold_dis functions...
Well, if you use my branch, I think I cleaned up everything, I think. Reccurance rules are pretty weird anyway.
I definitely recommend using platform.io though, if nothing else, it's easier to pull in forked libraries with.