Both Stky or Lala store their user data on your device. The data you create—tasks in the case of Stky, and log entries in the case of Lala—stay on your phone. If you back up your phone to your computer or the cloud, that data will be backed up as well.
One partial exception: If you accept Reminders access in Stky, it will sync its data with Apple’s Reminders app: reminders from Reminders will appear in Stky, and changes or additions made in Stky will sync back to Reminders. This allows you to keep your tasks in sync across devices without any explicit data storage from Stky.
Both apps use a small number of third-party services for analytics and crash-reporting purposes. That means they anonymously track your behavior so I can learn more about how people use the apps. Again, your actual content is not involved; for instance, I can see that someone in San Francisco created three tasks yesterday but have no way of knowing what those tasks were.
This behavioral data will be used for two purposes:
To better understand, in aggregate, how people are using the apps.
I work for an analytics company, Heap, as its head of design. My colleagues and I will also use this data to debug and improve Heap’s products.