I go for text in Markdown format, written with a normal code editor (VS Code) + pandoc (for producing a PDF) + git (for versioning).
These are all open source, high quality, freely available tools and a simple, human readable format.
Why don’t I use Word? Or Google docs? Or Scribus or some other handily packaged tool with lots of widgets for writing? First, I’ve been burned enough by Word crapping out when the document gets big enough that I just don’t trust it. Second, I will never trust my precious writing to a complicated, proprietary binary format. I know that .docx is some kind of XML which is nominally an open sourced specification, but honestly XML?! I don’t think this is better. Plaintext files with minimal, non-intrusive markup is what I find best, and Markdown fits the bill perfectly. git allows me to revision my work and many online git hosts have beautiful tools to check diffs. VS Code gives a word count and spell check and has a thesaurus plugin.