If you would like to download the client for Arkheim - Realms at War, please visit https://arkheim.com/en/#downloads.
At the moment, only Windows client is available.
The client offers you the same functionality as the browser version, however, video ads and the payment shop will still open in an additional browser window. Using the client might help if you encounter performance problems.
Please note that if you had the Arkheim Launcher previously installed, you need to manually delete it completely before re-installing, otherwise you will be stuck with an outdated version.