Over time LibreOffice worked on the concept of the Notebookbar, and that got supported by the working with Glade-designer for the user interface. With it's tabbed view, it looks as a notebook ;)
The Notebookbar itself also has multiple forms: Tabbed, Contextual Single and Contextual Groups. It can easily be seen in the next 5.3 release, if experimental features are turned on. The official 5.3-release is end of January.
LibreOffice offers an ideal solution for people that prefer to work with either a menu, or with a side bar, or with a more block-like interfaces!
*) Info Glade-designer
*) Download LibreOffice 5.3 bèta 1