Everyone's favorite "pretend you're exscaping a horde of zombies and get fit while doing it" simulator, Zombies, Run!, has just gone free. And not the on-sale kind of free, either - it's completely shifted to a freemium model.
First off, don't panic if you already own the app. Six to Start has stated that existing paid users will be able to access every mission through the end of the third season (along with Race Missions, Interval Training, and Story Missions) without spending any more money. It's their way of saying thank you to everyone who's supported them over the years.
New users can download Zombies, Run! for free, and will be able to unlock one new mission per week for free. Or they can get a Pro subscription for $19.99/year for unlimited access to everything. Current users will also need to go Pro if they don't want to wait to unlock missions in Season 4, but they'll only have to pay $7.99/year.