Here is the full list of all 25 Zombie Exodus achievements.
Ending 9 - Settle in Temperance
High humanity.
Ending 4 - Hidden Bunker
True romantic relationship.
Leave the cathedral solo.
Low humanity.
High allegiance.
High morale.
Best friend to all.
High dexterity.
High strength.
High intelligence.
High will.
High charisma.
High technical.
Find all hidden weapons.
Ending 1 - The Summit
Ending 2 - BayTown
Ending 3 - New Command
Ending 5 - Become a Zombie
Ending 6 - Become a Raider
Ending 7 - The Chosen
Ending 8 - Develop the Vaccine
End with all female survivors.
End with all male survivors.