Some information came out recently that indicates Left 4 Dead 3, a popular shooter series from Valve Software, could be in the works.

Valve’s Tristan Reidford has lightly teased Left 4 Dead 3 in a tutorial for the Destinations Workshop Tools.
The eighth image in the tutorial, titled “08_directory_fun.png,” showed a conveniently placed folder called “left4dead3.”

From the pessimists perspective, this was just a mistake, but it’s too convenient that the folder viewport was scrolled exactly so that left4dead3 was shown first.
According to Tristan’s Valve Developer Wiki contribution history, the image was first uploaded on June 28, and then nearly 24 hours after the community noticed the tease, was replaced by a poorly Photoshop’d version to remove the Left 4 Dead 3 reference.

Tristan’s Valve Developer Wiki contribution history:
* 17:59 (-8 GMT), June 29, 2016 . . File:08 directory fun.png ‎ (Tristan uploaded a new version of “File:08 directory fun.png”) (current)
* 13:49 (-8 GMT), June 28, 2016 . . File:08 directory fun.png ‎

Tristan Reidford and other Valve developers have been “playing” a lot of Left 4 Dead 2 recently. Currently, Tristan’s Steam profile says he’s played about 348 hours of Left 4 Dead 2 in the past two weeks. Also, Valve have released at least five updates this year alone for the franchise.

Source: http://www.neogaf.com/forum/showthread.php?t=1241044