I created the Left 4 Dead stats plugin out of a need for a L4D-oriented stats program. Existing stats programs such as HLStats don't really fit the needs of a co-op game like Left 4 Dead. I developed the co-op stats over the course of several weeks before public release while doing public beta testing at F7Lans.com. Right now I am currently testing the Survival stats.
You can find more information about the L4D Stats here on the plugin release page at AlliedMods. This will be the primary location for updates and release information.