Scrivener, a creative writing app (https://www.literatureandlatte.com/scrivener/overview). I've tested most if not all Libre alternatives and, well, they all lack behind. More or less badly.
Don't get me wrong, I appreciate those Libre alternative exist but writing is the one domain where I don't want to have to tweak, to search for workarounds. I just want so sit in front of the keyboard and type while still being able to write in a non-linear way. Scrivener gives me just that.