The Left 4 Dead 2 Authoring Tools are a set of software utilities that allow you to create your own levels, campaigns, common Infected, and other gameplay elements. They include versions of Source SDK tools that have been updated to work with the Left 4 Dead 2 version of the Source Engine. The Left 4 Dead 2 Authoring Tools are freely available on Steam to all owners of the PC version of Left 4 Dead 2. For the Authoring Tools to function correctly, it is important that your installation of Left 4 Dead 2 is fully up to date. You can make sure of this by running the game before launching the Left 4 Dead 2 Authoring Tools. The Left 4 Dead 2 Add-on Support is no longer needed and can be safely removed. Assets from L4D1 are now included by default.

Original version is now restored and remains the one true official merger
"King David" forgot to update his "Volume 3" version on "Game Maps" site
Workshop versions were now used as the base for current latest updates
"Scripted" version remains separately available like previously explained

Reverted back to official version collaboration with Rayman1103 and KingDavid2213
Script version from Art//An is now available separately due to concerns with online compatibility

Reverted back to official version collaboration with Rayman1103 and KingDavid2213
Script version from Art//An is now available separately due to concerns with online compatibility

Reverted back to official version collaboration with Rayman1103 and KingDavid2213
Script version from Art//An is now available separately due to concerns with online compatibility

Reverted back to official version collaboration with Rayman1103 and KingDavid2213
Script version from Art//An is now available separately due to concerns with online compatibility

Reverted back to official version collaboration with Rayman1103 and KingDavid2213
Script version from Art//An is now available separately due to concerns with online compatibility

Reverted back to official version collaboration with Rayman1103 and KingDavid2213
Script version from Art//An is now available separately due to concerns with online compatibility

Reverted back to official version collaboration with Rayman1103 and KingDavid2213
Script version from Art//An is now available separately due to concerns with online compatibility

will continue further investigating regarding its legitimacy
quick and easy to remove if the changes aren't necessary