The mod that is based on the leaked HL2 episodic mappack.
You can try over 60 maps made by Valve for both Half-Life 2 episodes in 2005-2007.

The author is Alex

Installation:
1) Download this archive
2) Extract it to your "sourcemods" directory
3) Install Source SDK Base 2013 Singleplayer in the Steam tools, right-click on Source SDK Base 2013 Singleplayer, select Properties, go to betas and select "upcoming -"
4) Restart steam