WP Tavern has a great review about the mentionable plugin

Mentionable is a plugin I’ve engineered (with all other amazing talent at XWP) while working on the 56th Grammy’s website.  It allows you to link content inline using the familiar “@mention” syntax. To read the full review, follow the link: http://wptavern.com/mentionable-plugin-adds-mentions-for-wordpress-content-with-inline-autocomplete