In past Misago used to have notifications feature but it was dropped during the grand rewrite of 2014. Since then I have planned to bring this feature back, but I've always had more important things to do, eventually resulting in this feature not happening.
Well, not anymore because the time is finally upon us and notifications are now priority thing I've started working on as we speak.
The plan is to implement new notifications framework for all Misago's notifications needs and for first release implement an MVP of notifications that only supports notifications about new replies to threads.
Notifications will live in
misago.notifications module and will cover both in-app notifications and email sending.
GitHub pull request with the work: #1536