manuskript - http://www.theologeek.ch/manuskript/
Downloads & Instructions https://github.com/olivierkes/manuskript/releases
(Similar category to Celtx https://www.portablefreeware.com/index.php?id=1349 - but manuskript is free and still being developed, while Celtx is now quite old and newer version are subscription based it seems)
Manuskript provides a rich environment to help writers create their first draft and then further refine and edit their masterpiece.
With Manuskript you can:
- Grow your premise from one sentence, to a paragraph, to a full summary
- Create characters
- Conceive plots
- Construct outlines (Outline mode and/or Index cards)
- Write with focus (Distraction free mode)
- Build worlds
- Track items
- Edit and re-organize chapters and scenes
- View Story line
- Compose with fiction or non-fiction templates and writing modes
- Import and export document formats such as HTML, ePub, OpenDocument, DocX, and more
Screenshot