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