Artemis(Lite/Premium/Coached/Prostaff) is an Android™ application that runs on mobile devices running the Android OS of version 4.1 (Jelly Bean) and higher. It can can only be installed directly from Google Play™.
Use your Android mobile device and scan the QR tag or click on the Google Play logo on the left. If it does not appear in Google Play for your device then you are running an Android version lower then 4.1. Artemis does not require any special capabilities of your mobile device's hardware except for the de-facto minimum device capabilities of having a touch screen. It currently supports more than 15.000 different mobile devices. During installation, the app requests access to Storage (for creating database backups) and Network communication (for linking up with Google Drive and Sharing results via different media, e.g. Facebook, Gmail, etc.).
See the Manual page for more information.
You can upgrade to the Premium version using the Help (?) menu on the main screen and then click Upgrade to Premium. Once you've upgraded to Premium you can further upgrade to a Coached version by using the same Help (?) menu on the main screen and click Upgrade to Coached. You will get a lot of extra features by upgrading as you can read here Upgrades
For those of you with iOS, there is no iOS version nor will there ever be. Sorry for that..