Zombies, Run (Free) has been inordinately popular since its release in 2012, combining fitness training with outrunning zombies. Now, the app is hoping to become more popular by shifting to free-to-play, and introducing a whole host of new features. Season 4 is the big new addition, bringing 40 new missions to play. You can play multiple missions back-to-back, the interface has been revamped, Spotify and Pandora support has been improved, chase difficulty is adjustable, and more little tweaks to improve the experience. Check out the new trailer:

For those who have paid for Zombies, Run before and are worried about the new free-to-play model, worry not: anyone who’s bought the app before will have unlimited access to seasons 1-3 and all paid add-ons. You can also play one free Season 4 mission for free, or upgrade to a special pro membership that unlocks all of Season 4 for $7.99 per year. New players will get the first four missions for free, with a new mission unlocked each week. Pro memberships for new users run $2.99 per month or $19.99 per year, unlocking all 200 story missions, along with Interval Training and Airdrop Mode.