Fitness app for coworkers

Is there a free app, for fitness for group of people.

For my job, I have 50 coworkers who we want to challenge to who walk more steps?

I want something that is user friendly, professional.

GymRats · Fitness challenge free but for IOS
makeuseof.com

There are many, you can check Google for more

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there are a lot of pedometers app some might also give you the ammount of calories your burn, most of cellphones have a health center or something like that includes a pedometer to count the steps and calories, you need to start searching on the play store for the app, for a free option you can go for Goolge fit: activity tracking.