Now free - Pandemic Express - Zombie Escape, a group of humans try to outrun a player-controlled swarm of infected. Everyone spawns in a train station until one is randomly infected and needs to turn fleeing survivors into zombies. Survivors try to escape by train.
Mod: This previously paid game is now free to play indefinitely. Marked as long running deal, not suitable for re-post in the future.
I think free and free to play is difference.