An add-on (beta) to turn LibreOffice and OpenOffice into a kind of an outliner (reminds me of that MS Word add-on which used to be around as an alternative to Scrivener to Windows - forgot the name):

https://github.com/XRoemer/Organon

The screenshots will give you an idea:

https://github.com/XRoemer/Organon/tree/master/Screenshots