Yes, it is a .NET desktop WinForms client.
The app uses a background task to update the Node State section of the form on a timed interval. It also knows how to send Ether (with or without extra data) between two accounts. The send Ether integration assumes you have more than one account configured in your Rinkeby geth.exe node. The app will prompt for your password the first time it is required.
In terms of failover, the app tests to see if geth.exe is running and will automatically connect (and reconnect) if geth.exe isn’t already running on Rinkeby. It also checks to see if the node is syncing and if so, the background task pauses until the sync completes.
Michael Herman (Toronto)