Termux:API is an Android add-on developed by Fredrik Fornwall that provides command line access to device APIs. With this add-on, users can read and send SMS messages, access the device GPS location sensor, and even vibrate the device when something interesting happens. Additionally, users can access the system clipboard from shell scripts and list contacts from the system contact list.

To use Termux:API, it is necessary to install the main Termux app and an additional package inside it. The available API commands can be found in the app's documentation. Overall, this add-on is a useful tool for those who want to control their device through the command line interface.