Flathub is the central place for building and hosting Flatpak builds.
To install applications that are hosted on Flathub, use the following:
flatpak remote-add flathub https://flathub.org/repo/flathub.flatpakrepo
flatpak install flathub <appId>
For more information and more applications see https://flathub.org
To install NEST Desktop application from Flathub, use the following:
flatpak install --user flathub io.github.nest_desktop.nest-desktop
Run it from the application desktop.