My latest side project is still in figure-out-how-to-get-users mode:

https://feelers.online/

The idea is to give content creators (authors, YouTubers, webcomics, bands, etc.) a way to inform their fans when new content drops. It also gives the fans a lot of control over how the notifications arrive.

I made this to address a problem I experience myself. I operate a website that publishes on an irregular schedule, and it can be hard to let readers/listeners know when we have something new.