well... it would require a custom component. first you'd have to add hooks for each event that you want to capture, for example, forum:topic:reply. Then your component would have to run some code to display the details for the item in whatever way you want on the newsfeed. If the event doesn't already add a notification you'd have to make it do that also. there's no built in way to do this though - you'd have to write a custom component. there are a few people on this board who do custom (paid) components/mods for Ossn, including myself. you can feel free to contact me about this if you like (email in my profile).

It's not really what I'm asking for. Unless you mean that such a system would add to wrong notifications.

I meant notifications in the top bar on the site.

https://www.opensource-socialnetwork.org/discussion/view/3475/users-are-notified-for-anything-that-should-not-be

OK, then how about notifications that something has been written instead?

Not sure what you mean in one flow but there is no easy way to handle precisely the forum, groups , in newsfeed page. Initially we did it in Ossn 1.x but removed it in later versions.