Hi Gomle,
BuddyPress is a plugin that allows you to create micro social communities around WordPress.
If you need activity, groups, friends, private messages etc from the site front you should use BuddyPress, otherwise you may not need it.
bbPress provides forum capability for a site. If you are only looking for forums, you should use bbPress.
Since the two projects have some common lead developers and both are under the wporg umbrella, bbPress has native support for BuddyPress. In case BuddyPress is active, bbPress allows using forums with group and integrates with user profile to enhance the experience.
Hope that clarifies.
If you are not using BuddyPress, The Live notification plugin won’t work. It depends on BuddyPress notification component.
About the subscriber, Yes, I believe it can be done with the aid of some code. All we need to do is write codes for
– Adding a notification to all the subscribers on new reply.
– Clearing/Marking read the notification when the subscriber opens topic
– Deleting notification if reply is spammed/trashed etc.
PS:- My reply is in the context of BuddyPress notification not the email notification.