Modal
A service that runs your code on demand in the cloud, useful for background or long-running work.
Think of a workshop that builds something when you place an order, then shuts the lights. Modal runs code for you when asked, then stops when it is done.
It matters because phones are limited and public apps cannot hold secrets. You move heavy or sensitive tasks to Modal, keep keys off the device, and respond to the app over the network.
In practice you write a function, deploy it, and get an HTTPS endpoint to trigger it. The app sends JSON to that address, Modal does the work, and you store keys as environment variables so they never ship in the app.