The Companion App run natively on an Android or iOS device. Current version of the app is 2017.11.11. You can download them with on each store:
Use the menu on the right side to chose what you want to do.
You can also connect the In/Out device to the Companion App.
Important tip: The communication between the device and the Companion app is done over Wi-Fi, the device being the HotSpot - the device is the "router" and you associate your phone or table to the device. You might have to jongle between your usual Internet connection and the device HotSpot on your phone or tablet.
From there, you can synchronize the statistics between the device and the Companion App (and the cloud).
You can mirror the In/Out device screen to the Companion App, you can upgrade the firmware, and you can access debug information in case of an issue.
Tip: If you think the screen of the In/Out device is too small, use the Mirror feature to mirror the screen to your phone or tablet.
You can also access the stats interface via a browser at https://stats.inout.tennis.