As the achievement detail explains, one needs to complete every Available Project in The Foundry. As you complete each project, it will become greyed-out in the list, with a notation of "Project Completed" in the project detail.
Please note, finishing all of these projects requires a sizable amount of these resources:
Elerium
Alien Alloys
Weapon Fragments
Various alien corpses
So, it might be smarter not to sell any of those items on the "Gray Market," until your projects are completed.
Here is a list of ALL 18 Available Projects to be completed in The Foundry:
Heavy Weapons Platform
Alien Grenades -- (requires capturing Alien Grenade)
Improved Medkit -- (requires Thin Man autopsy)
Improved Arc Thrower -- (requires researching Elerium)
Advanced Repair -- (requires Heavy Floater autopsy)
S.H.I.V. Laser -- (requires researching Beam Weapons)
S.H.I.V. Plasma -- (requires researching Plasma Rifle)
S.H.I.V. Repair -- (requires researching EMP Cannon)
Drone Capture -- (requires Drone autopsy)
Ammo Conservation -- (requires Muton autopsy)
Advanced Flight
Advanced Construction -- (requires Sectopod autopsy)
Improved Pistol I
Improved Pistol II
Improved Pistol III -- (requires researching Plasma Pistol)
S.H.I.V. Suppression
Stealth Satellites -- (requires researching Alien Nav Computer)
S.C.O.P.E. Upgrade -- (requires researching Weapon Fragments)