wpForo User mentioning addon is a lightweight solution for wpForo forums to easily select users when you want to mention them in topic and post editors. It popups a small window with an autocomplete list of users while you’re tying, starting with @ symbol. The pop-up window allows you to go through all suggestion using the up and down arrows of your keyboard and select the one you want by pressing the enter button.
The mentioned users will receive an email notification letting them know about the topic or reply where they were mentioned. You can find the settings to control user mentioning notifications in wpForo > Settings > Subscriptions & Mentioning admin page.
If this option is enabled, users will receive email notification when someone uses @nickname of the user in posts. You can manage the email content in this admin page as well. Users can mute the mentioning emails from their profile page: