Here is the full list of all 14 Concurrency achievements.
Finish a single hall
Finish ten halls in one sitting
Finish fifty halls in one sitting
Get the most expensive upgrades for the gun and sword
Get an electric chain kill
I mean, who'd even notice you're gone?
Escape the purple haze
Piece together the puzzles
Blast your way through the swamp
Reach the loading dock
Grab your gun and bring the cat in
He can't have gotten far, right?
Take the scenic route
Beat the game