Release 1 of the mod. Consult this download's description or the mod's ReadMe.txt for a detailed list of all content contained in it.
To install, extract the folder 'HL2-Aftermath' to this directory:
C:\Program Files (x86)\Steam\steamapps\sourcemods\
Or, where ever your Steam installation is, then \steamapps\sourcemods\
Then, restart Steam. It will appear in your Steam Games list as "Half-Life 2: Aftermath"
Note: This mod also requires Source SDK Base 2013 Singleplayer, with the beta branch set to "upcoming".