Stibium is desktop enviroment based on cloud storage and designed to run inside a web browser. It was built as an Ubuntu One app, but it could work with NextCloud
Stibium is a web application that provides an interface similar to a traditional desktop environment (it imitates KDE) but uses a cloud service to store your files. It can be seen as a desktop environment to manage your files on the cloud.
We use the Ubuntu Font (Ubuntu Fonts) because is a free font, and it’s very nice.
Source code: https://invent.kde.org/unmaintained/stibium