I have a very, very long list of fun electronics projects for weekends that never seem to materialize, but this might rocket to the top. The Ollee Watch is a drop-in PCB replacement for the Casio F-91W and A158W that turns these classic watches into bluetooth-enabled smart watches. It has weather, some health metrics like heart rate monitoring, alarm snoozing, and time sync right now. $60 for the board itself, $100 for the complete watch.
Ollee Watch
Bookmarked: https://www.olleewatch.com