It's not Left 4 Dead, but it's still worth trying out! Shaders, source code and tools have all been updated.
Posted by Varsity on Mar 16th, 2009
Among many changes, this beta update allows shaders to be compiled for the Orange Box, fixes various command line tools, and adds a new 'template mod' with lots of common teamplay features that aren't part of the old HL2 Deathmatch source pre-written.
Access the beta through Steam's settings page.