Now Facebook wants to encroach on one of the remaining features unique to Twitter: the hashtag.
Facebook is working on incorporating the tool, which on Twitter allows users to group trending topics for easy discovery using a pound sign, like #newpope, when the Vatican announced the election of Pope Francis, or #CPAC, for the ongoing conference of conservatives.
According to the Wall Street Journal, incorporating the hashtag would help users stay on the site longer as they explore trending topics. More time on the site, naturally, means more ad revenue for Facebook.
The Facebook-Twitter turf wars are undeniably escalating. Most recently, Facebook blocked Twitter's new video-sharing service, Vine, which was largely seen as a response to Twitter blocking photo cards after Facebook purchased Instagram.
Facebook also added user tagging -- similar to Twitter's incorporation of the "@" sign to live-link user's handles -- and created Twitter-like subscriber lists for categorizing groups of friends.
For its part, Twitter has added richer media within the timeline, with Facebook-like "cards" displaying a content preview. Twitter's timeline is a riff on Facebook's integral newsfeed.
The hashtag is unique, however, in that it initially came from the users themselves. It gained wide use in 2007, when a California resident began grouping tweets related to the San Diego wildfires, and the site began to hyperlink hashtagged words to assist with searches and trends in 2009.