If you do automated tests through Appium on mobile devices, you know how annoying it is to do the setup every time, for every device. AltRunner does this setup automatically whenever you plug in a device. You can also run tests in parallel on multiple devices. In its enhanced reporting module you can investigate failed tests. AltRunner has been a huge time-saver for several projects where we do cross-platform automation tests.
You can write the tests in java, python or C#, and the runner will do what it knows best, to run them on targeted mobile devices. This is the alternative to cloud device hosting if you already have the devices in the office, and you just want an easier way to do the setup, organise your test runs and analyze results.