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