Zombocalypse is killing zombies by the numbers.
You start with a machete and are tasked with hacking your way through as many zombies as possible while stuck in a single 2D environment.
If it's a farm you'll get zombies with pitchforks. If it's a zoo you'll see gorilla zombies. If it's a prison you'll get, yep, zombie prisoners.
If you survive long enough you'll get a boss zombies to take on as well. You'll want to save up a kill streak reward for these, such as the airstrike, which you get for killing zombies in quick succession.
Anyway, whether you survive or not doesn't matter too much - it's all about racking up numbers of zombie kills.
This undead body count is persistent across each attempt. Increasing that number levels you up and unlocks more weapons.
But you'll need coins (collected from the undead) to buy upgrades and new guns.
And so it goes: you kill, you die, you spend, you get bigger weapons, you repeat.
If you want to throw yourself into Zombocalypse then you can purchase it for £1.49 / $1.99 on the App Store.