[griffindor]

AsteroidOS, which runs on many Android watches, and offers a Linux environment over SSH and WiFi (for watches that support it). https://asteroidos.org/

The simplest integration is writing a daemon (in the language of your choice) that schedules wakes, syncs, and sends FreeDesktop notifications.

If you want more of a UI, then you'll be writing QtQuick, which is QML/Javascript/C++.

Their best supported watch is the TicWatch Pro: https://asteroidos.org/watches/catfish/

[Sateallia]

I have a TicWatch Pro (catfish) running AsteroidOS nightly. If I turn Wi-Fi on, (understandably) its battery drains fast and it gets kinda hot so I leave it off. (I don't know if this is the case for other AsteroidOS watches.) I personally wouldn't recommend it for this specific task even though it's great for anything else.