The Nightmare never ends. Nearly three years after Outbreak: The New Nightmare released on Steam Early Access, major new features are still being added!
Outbreak: The New Nightmare 7.0 has been released. It includes the following enhancements:

• Local 2-player co-op is now available. Access it via the Local Game menu (replacing the Single-player menu). You can customize the controls for both players in the Options -> Controls menu. See this post for details. NOTE: Local co-op is experimental and you may encounter bugs or other unforeseen issues. PLEASE report these to me on the forums or via the official Discord instance so I can address them. Local co-op is DEMANDING on your machine when on high quality levels as it's rendering everything twice. If you experience framerate issues, lower your graphics settings and try it again.
• Numerous performance improvements across the game. Using a new garbage collector which should reduce the amount of hitching experienced during gameplay on mid to lower-end hardware. You should also see minor framerate improvements across the board in single-player and online co-op.
• Upgraded the underlying engine to the latest version. Although this doesn't seem like a major note, this was actually extremely hard to do due to the age of the codebase, as well as how I architected it originally. Successfully updating the engine will allow me to keep pushing forward on new features and fixes, as well as update the console versions and target new consoles in the future!