Tag Subscription and notification feature

Firstly I appologize if this exists as feature or post here in community, but the tag based posts did not quite fit the idea i was looking forward toward, which is:

1) ability to create tags and let members subscribe to those specific tags
ie: #anime #cars #catsfunny
2) when a person uses the tag in a post the user is notified same way that the @role notification works
3) the key point is to let users add/register themselves to tags they are interested without affecting role organization and possible over exhaustion of role strictness.

Maybe there is a bot that achieves this?
Thanks for listening in :)