Basically this is an easily self-hostable, partial clone of ntfy.sh that sends messages to Matrix rooms.

It can run standalone locally, or it can be run as a service that listens to HTTP requests similar to ntfy.sh.

I setup a service myself running at @pokem:jackson.dev, but that will likely fall over if this becomes popular.

It works by using the Matrix room ID instead of ntfy.sh's custom topics. Invite the bot account to a Matrix room, then send the service the Room ID and the message you want via HTTP, and it will message the room.