Ismail

Does the same functionality as BuddyPress, emailing users who get mentioned in a bbPress topic or reply. The aim of this plugin is when to enable that feature when no BuddyPress is there. 
To do: – warn user about bbPress/BuddyPress presence

bbPress Mentions Email Notifications

Adds the @mentions to bbpress - really useful

Great plugin

Email bbPress topic/reply mentioned users, set custom email and some basic settings

Jesper Johansen (jayjdk)

Twitter Profile Field is a simple WordPress plugin that gives the user a new field in the profile page to add in their Twitter username.
The pluhin also provides a shortcode which allows authors to display their, or others, Twitter usernames, optionally with a link, in posts, pages, and text widgets.

Twitter Profile Field

Adds an additional field to the user profile page where the user can enter their Twitter username.

bbPress Mentions Email Notifications vs Twitter Profile Field