Babbel adapts the app UI to users' characteristics (e.g. here with the language the user is willing to learn).

In the second step of the onboarding, the user is asked to pick his favorite colour to customize the UI of the app. It's a way to personalize the experience and increase the perceived value of your product. Implemented during the onboarding, this trick can increase your conversion rate when you show a paywall at the end of the onboarding.

Daylio is a journaling app. During the onboarding, users can pick the colour set and the emoticone set that they prefer. Implemented during the onboarding, this trick can increase your conversion rate when you show a paywall at the end of the onboarding.

Calm is a meditation app. As part of navigation' settings, you can customize what Calm calls "Scenes". Scenes form the background of the app which is both a dynamic image and a background sound. A simple trick to personalize the user experience and to put him/her in the right mood to consumer your content.

Loona is an app to improve your sleep. During the onboarding, users can pick the colours they prefer and these colours will be colour palette used in the app. Implemented during the onboarding, this trick can increase your conversion rate when you show a paywall at the end of the onboarding.

In FitnessAI, push notifications look like a chat with a personal coach which you can change the name. Another way to create a special relationship with users and make them come back on the app.