Once users accumulate enough number of coins, they can spend it in the app and the company plants a real tree in the world through another partner non profit organization. It makes a real world impact in exchange for users’ focus on their activities - the core utility of the app.

Once users unlock a new species of virtual tree through premium subscription, they do not want to let it just sit in their inventory. Instead they want to make use of it (plant it in their virtual plot of land). Hence, they commit to their activities and plant those trees in their plots - the app keeps the users engaged by using behavioral psychology.

When users plant one tree during their onboarding phase, to learn how the app works, something interesting happens. The virtual plot of land has multiple square divisions where the trees can be planted, and one of those squares get occupied by the planted tree. This drives the users to make every square division occupy a tree. This is again behavioral psychology at play. We tend to complete what we have started - Zeigarnik effect. When users look at only one square occupied, they tend to complete filling up all the squares. That is not only delightful but also it enables the product achieve its main utility - to help users keep focusing on their activities repeatedly, forming a habit of it for them.

Forest app provides real value to the users, encouraging them to take the premium membership because of reciprocity - humans tend to feel obligated to return favors, gifts, values, etc.