I very rarely purchase any apps for phones, most of my gaming is done on console or PC but Zombies, Run! from Six to Start is one of 2 apps I've purchased ever and I wanted to share my love of it. It is a training app for runners whether you're training for your first half marathon or you just want to run. Its a story of how you become Runner 5 of Able Township who goes out on missions during the zombie apocalypse. You can listen to your own playlist in between the story and even set zombie chases where a horde will come after you and you have to run faster or it will catch you. I listen to it when I trail run in the woods and it makes for a nervous environment especially with ambient zombie noises coming through.
If you're looking for a reason to get out and run and enjoy a good zombie story, you should really look into this. There is a free verison allowing you to try it out but there is plenty of content in the paid version. There are currently 5 seasons, each season could have 30 missions and each mission range from 20 mins to 40 minutes long. I love it!!