Here is the full list of all 43 Over 9000 Zombies! achievements.
Participate in a multiplayer game.
The zombie world is independent of our will.
Abused patience turns to fury!
Health is the greatest gift, a close second is BRAINS!
Get 30 kills per second!
Terror possessed me then!
Zombie Napoleon meets his zombie Waterloo!
Kill over 1000 zombie eyes!
If only he had the body of a horse...
Voted the greatest zombie of all time!
Vote for Zombie Thomas Jefferson, or don't.
Derail the Waltz of the Undead!
Collect 100 Power Ups!
No 8th symphony for zombie Sibelius!
Kill over 1000 crabs!
A jail is an isolated system.
Blood and Flesh can be trusted.
The army of the undead will march at daybreak!
Kill 9,000+ Zombies!
Kill over 1000 zombie dogs!
Decreased Zombotropy.
Quoth the Raven "Nevermore."
Get 15,000 damage per second!
Kill over 1000 zombie crows!
Don't call me slow!
Your world didn't end!
You didn't donate your organs...
It didn't taste like chocolate ice cream either...
Not a wimp.
Lots of progress!
You watched the world burn, and survived. It was kind of cool.
Kill 1000+ Zombies!
Construct a turret from scrap metal!
Green IS good.
You won that race.
Making some progress...
Get 5,000 damage per second!
Get 10 kills per second!
The first day is always the hardest, except in this case, it's the easiest.
Kill 90,000+ Zombies!
Kill 900,000+ Zombies!
Construct 100 automated turrets.
Construct 1000 Turrets from random scraps of metal!