Coronoro

Simple Plugin which shows whether a registered user has read a Post or not. 
You can also choose to show the number of unread Posts at Forum level. 
This Plugin is an update to the older <a href="https://wordpress.org/plugins/bbpress-unread-posts/" rel="ugc">bbpress-unread-posts</a> Plugin.

bbPress Unread Posts v2

Simple Plugin which shows whether a registered user has read a Post or not.

normen

Shows a label for unread forum posts. Marks topic as read when user visits the topic. 
A “mark all read” button on each page allows setting the topics on that page as unread. 
Based on a plugin by 3sixty, however not much code is left of it 😉

bbPress Unread Posts v2 vs BP Unread Posts