Valve have released a beta of L4D2.
It contains a new scripting/mutation system that allows for new gametypes. Several are included, but the main point is that modders can do much more now.
But it also contains Linux support. Huzzah!
If you’d like to have a shot with me, the beta is available if you own L4D2 already.
The catch? It’s 18 f***ing GB. So hopefully you’re with an ISP that gives you unmetered Steam downloads (like me).
Let me know if you get this version, and we’ll sort out a time to play co-op online.