This is pretty awesome (and free). It's called Treecard, and they partner with Ecosia to plant trees. 10,000 steps = 1 tree planted. Based on the (albeit limited) research I've done, it's legit. Great motivation to get up and move!
Referral:
Join me on Treecard - the app that reforests the planet with your everyday actions. You'll plant 1 tree and earn 50pts (for free!) when you sign up. Use the referral code
dan-j30 to get started.
https://treecard.app.link/refer-a-friendThe referral earns points to use toward eco-friendly brands and whatnot, but hopefully can use them to plant even more trees or use some of their other features.
I'll post with any updates!