Here is the full list of all 68 Zombie Army Trilogy achievements. It takes around 30-35 hours to unlock all of the achievements on Windows.
Complete any Campaign chapter in 4-player co-op at any difficulty level
Revive other players 50 times
Reach at least Wave 10 in Horde Mode – Flood of Tears
Sever 10,000 limbs
Reach at least Wave 10 in Horde Mode – Waves of Despair
Save the man in the hospital
Reach Wave 10 in Horde Mode – Dead Man's Bluff
Put the tortured souls in the Forest out of their misery
Kill 50 enemies that are actively attacking other players
Kill a total of 20 enemies while incapacitated
Become possessed
Kill 25 Fire Demons
Reach at least Wave 10 in Horde Mode – Cathedral
Kill 50 Super Elites
Kill 100 Zombie Snipers
Successfully complete Army of Darkness
Kill 500 Skeletons
Kill 25 Summoners
Loot a Chainsaw Elite's corpse
Successfully complete The Keep
Shoot the 3 Zombie Ravens outside the Folterschloss
Kill 5,000 enemies of any kind
Reach Wave 10 in Horde Mode – Dead End
Successfully complete Forest of Corpses
Successfully complete Freight Train of Fear
Successfully complete City of Ashes
Kill a Survivor
Successfully complete Tower of Hellfire
Successfully complete Terminal
Get at least 20 for 1 with an explosive kill
Successfully complete Crucible of Evil
Pick up a phone
Complete levels as every playable character
Successfully complete Gateway to Hell
Reach a total shot distance of 50km
Kill 20 enemies as they revive
Successfully complete Purgatory
Get at least 15 for 1 with an explosive kill
Get a 5-for-1 kill with any sniper rifle
Successfully complete Subway to Hell
Kill 50 Suicide Zombies
Successfully complete Library of Evil
Kill a Suicide Zombie by hitting his grenade
Get an unbroken 10-headshot streak
Successfully complete Labyrinth of Death
Kick 50 enemies down
Kill a Zombie Sniper in mid-air
Get at least 10 for 1 with an explosive kill
Sever 1,000 limbs
Headshot a Heavy Armour Zombie without removing his helmet
Reach a Chain Count of 30
Defeat 500 enemies with headshots
Successfully complete Cathedral of Resurrection
Kill an Occult General
Successfully complete Village of the Dead
Loot a Super Elite's corpse
Pick up a Panzerfaust
Pick up the Preacher
Reach a Chain Count of 20
Reach a Chain Count of 10
Successfully complete all Chapters on Sniper Elite difficulty
Score 5,000 with a single sniper round
Reach at least Wave 10 with the highest score in any Horde Mode map
Reach at least Wave 10 with more gold medals than your companions
Kill 20 Elites in co-op
Complete every Survivor sidequest
Collect every Gold Bar
Find and shoot every Bottle of Blood