The nymea:app is the official community client for the nymea server.
The source code of the client can be found here:
You can get the app from the GooglePlay store.
You can get the app for your iOS device from the App Store.
You can get the nymea:app snap from the Snap Store.
There is a Microsoft Windows installer available, which allowes you to install nymea:app on your Windows PC.
If you want to use the nymea:app on macOS, you can download the latest bundle from here: