Like others, I use whatever text editor I find most convenient and write it in Markdown-like syntax (on Windows, that's MarkdownPad). When I want to get it into PDF, I'll either use Leanpub to make it into an eBook, or I'll convert it into LaTex and use something like http://overleaf.com (wysiwyg preview of your LaTex) to improve the formatting (or do things that Markdown-like syntax doesn't handle).

Abiword is a lightweight word processor. You'd probably want to use Abiword's template feature to set defaults to what you want. EG I prefer light text on dark backgrounds. I like monospaced fonts. I have all the toolbars turned off.

This allows me to do basic "text editor like" typing, but with the option to apply styling and export to PDF.

http://www.abisource.com/wiki/FaqDefaultFont

http://www.abisource.com/wiki/FAQ/Always_save_as_Word

Otherwise, any text editor you like for most of the stuff and the tools you need for the other stuff. gedit for all the texty stuff, and then import it into a WP to apply styles and export to PDF.

I guess I misunderstand your question: why don't you just use a word-processor for everything, and save as text? Why don't you just use a text editor and then import into a WP when needed?

I don't want to use a word-processor at all. But thanks for the input on abiword

I use several things:

leanpub: for writing books. uses Dropbox, web services to produce books from markdown. I can edit markdon files on my phone, ipad, Chromebook, and kaptops.

Google docs: quick notes that I might need in the future; having search helps find stuff later

Microsoft OneNote - for notebooks for travel planning, research, etc.

Emacs: org mode, but it takes effort to get started

http://www.latex-project.org/ ?

Isn't big and clunky like docbook?

Well, the example on the site show it can be pretty simple (I never had use for it, so I never really tried it ), and formatting could be easely added by editing a classic text file...

So the machine that would convert latex to PDF doesn't have to be the one the text files are written with.

TeX (and LaTex) is pretty old, and designed to run on machines much less powerful than what we have today. Back then, I've used LaTeX on MSDOS PCs with 640 kB of memory. And the original TeX was written in 1978 for a PDP-10.

Many distributions are indeed big and clunky because you get lots of packages and fonts all in one, and there's no good way to selectively install.

Or do you mean verbosity when writing the markup? Actual text doesn't require a lot of markup, and you can make things even simpler by defining your own commands.

I use BBEdit for its text-only and RegEx and really enjoy it. I must admit, I do like MS OneNote as I can write a note and see it on all my devices.

https://www.zoho.com/docs/writer.html - Check this out?

Still an word-processor, one could have mentioned google docs too.

And I would like it to be open source too and not a web application

emacs

http://www.danfowler.net/resources/emacs_talk/#/