The app is “Note Everything”, linked.

Most widgets are available, however one widget is (unfortunately) named “Folder”. I see it in the trebuchet add widget screen, but cannot find it at all in LL add widget list.

Fortunately, the app’s interface provides a means to add a widget to the desktop; however it’s much nicer to be able to add a widget e.g. within a LL folder, rather than having to move it there.