Here's another anniversary, a Tripwire Interactive celebrates 10 years of Killing Floor, as the first installment in their zed shooter series was initially released on May 14, 2009. They mark the occasion by noting that more than 15 million unique players have played games in the series, which has earned over $100 million USD over the past decade. Here are some details:

Today, publisher and developer Tripwire Interactive celebrates the 10-year anniversary of the Killing Floor franchise. Since the horror based co-op first person shooter first launched on May 14, 2009 for PC on Steam, the Killing Floor franchise, including the original Killing Floor, Killing Floor 2, and Killing Floor: Incursion, has sold nearly 10 million units, earned over $100 million in franchise revenue, and has been played by over 15 million unique players worldwide.

Speaking to VentureBeat last year, Tripwire Interactive Vice President Alan Wilson attributes some of the long term success of Killing Floor to the studio’s efforts in providing regular and free content updates to players and Tripwire’s roots in the modding scene. “With Killing Floor, we’ve added all sorts of new things over the years,” said Wilson. “We started with seasonal events, which have been wildly successful. We also introduced new weapons, new game modes, new characters, etc.”

To-date, Killing Floor 2 players on PC, PlayStation®4, and Xbox One have seen numerous free seasonal updates that make painting the town red with blood feel fresh, with over 49 new maps and 139 mad scientist weapons and more on the way.

To celebrate 10 years of Killing Floor, Tripwire Interactive has released a fun infographic highlighting some of the series’ major milestones and player achievements. PC players can also look forward to a major Tripwire Interactive Steam publisher sale that starts later today and runs through Monday, May 20, 2019. The Tripwire Steam Publisher Sale will include deep discounts on the entire Tripwire Interactive Steam catalog including last week’s Spring Content Update for Rising Storm 2: Vietnam.