ZRX hosts the main version of Zombies, Run!, which includes all of the main story content from Seasons 1-10 as well as zombie chases, base builder mode, and more. Missions can be unlocked on a 1-per-week basis as a free user, or you can purchase a subscription for unlimited access to all content for the duration of the subscription period.
Zombies, Run! 5k Training is a separate app, containing 24 custom workouts designed to take you from 0 - 5k over 8 weeks. All the content in the 5k Training app is unique, and does not cross over with Zombies, Run! (with the exception of the first S1 mission which is included as "The Story Begins"). It does not contain the base builder mode or zombie chases. Workouts must be unlocked with a one-off in-app purchase.
For more information, check our Zombies, Run! 5k Training help guides.