Recently, Left 4 Dead developer Mike Booth reminded of himself again. He addressed the L4D community and talked about working on a new project.
This will be a 4-player co-op shooter, created "based on what made L4D special."
The project is still in its early stages, but they are already preparing to conduct playtests and invite players to register:
«If you liked the teamwork, tension, and replayability of my past games, you'll probably find this one interesting. It expands the co-op formula in a way that I've long wanted to explore.»