Tools for Writers and all Free

Everything Ebooks (EE)
          EE is a free app for authors to write ebooks while inside an ebook, but it can also create ebook covers, instantly generate a .epub file with a viewer, offers alternative enhanced/immersive ereaders using Scenecraft for audio and images, handles .docx files, if desired it offers AI editing assistance via your AI API key (optional), and now with some PDF stuff too, even square 8.5 inch pdf's.
All of that with total privacy for all of your writing, as it is stored local to the web browser that you are using. There is no cloud storage, but it does offer Export/Import of all writing (text, images, audios) as .zip files for backups or sharing with other devices.
This app can be used offline (no wifi/internet) after landing on the first page.
It can also be installed and used locally for those who have set up a Node.js, Next.js, and React environment.
As a long time user of Atticus and Vellum, both are great but expensive for what they offer, I find EE just offers more features, it's very fast, and it's results publish perfectly to Amazon's KDP (sadly the gold standard).

Book ID Mint - a book ID for all booksellers
Passages Builder - create interactive nonlinear stories
EPUB Xray - see inside your ebooks
Encoded Prompt Decoder - base64 + gzip to human readable
AI-isms - detect common AI-isms in text; manage your dictionary
Text to Word Frequency - count occurrences of each word
Semantic Grounding with .html download
Readability (Flesch, Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau, Automated, Dale-Chall, Linsear) with .html download
 
Converters:
DOCX to plain text with .txt download
EPUB to plain text with .txt download
EPUB to HTML with .html download
JSON to readable with .json download
Markdown to plain text with .txt download
PDF to plain text (but it does not remove the page headers/numbers) with .txt download
Text .txt to HTML with .html download
Text to Vellum to DOCX with .docx download
wrap paragraphs - to copy/paste for: reading (wrap paragraphs at 70 characters)
unwrap paragraphs - to copy/paste for: Vellum and TTS audio (it's easier with Chunks below)
Text to proper Chunks (of 1000 to 5000 characters) for TextToSpeech (TTS) audio
helps debug DOCX by viewing HTML blocks (for example: p, h1, h2, and so on)

download is not from a server, rather it's directly from the page in the browser, same as a local save.

Any sufficiently advanced technology is indistinguishable from magic. Arthur C. Clarke