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