In my subjective opinion, NovelWriter is one of the finest FOSS writing programs out there. It has enough features for organizing, notes, etc, to be more usable than a text editor, but without the (IMO) unneeded complexity of bigger programs such as Scrivener. It really gets out of your way and lets you get to writing.

It also has been extremely stable and glitch-free in my experience.

If you're okay with not having a WYSIWYG rich text editor, I'd highly recommend giving it a shot. :)