The whole content of your CERNBox space is fully accessible from SWAN. If you click on the CERNBox tab, you will be able to browse your files.
If you click on notebooks, the notebook interface will open to edit them. Similarly, an editor appears when clicking on files with textual formats.
By browsing through your CERNBox, you can create notebooks inside regular folders that do not belong any project, if you wish so. The only drawback is that you will not be able to share those notebooks from SWAN, since projects are the unit of sharing.