You have a great idea for a Kindle book, and no idea how to organize your thoughts and get them into a format that is Ebook-friendly. While you will still need to go through Amazon's upload process and have your book in the correct PRC format to do so, these paid and free programs can put you on the right path to that goal.

LibreOffice Writer – Word 2007 type interface and lots of little extras like auto-completion, spell-checker, and auto-formatting. Advanced options too such as, footnotes/endnotes, embedded images, indexes and more. Free to download and use. http://www.libreoffice.org/discover/writer/

The Sage – A dictionary and thesaurus in one, The Sage offers a pronunciation guide with audio, synonyms, definitions, example sentences, anagram solver, search storage, and more. Free to download and use. http://www.sequencepublishing.com/thesage.html

Sigil – Geared toward the e-book author, Sigil offers a WSIWYG editor, search tool for text and formatting, table of content and index creation, and a validator to make sure you are meeting EPUB standards. Free to download and use. https://code.google.com/p/sigil/

TreeSheets – Fascinating outlining program that allows you organize data in 'branches' of information. Almost a spreadsheet format, but with a twist. You may include images, data, text, and more inside each cell. There is a learning curve to using it, but once you overcome that it will be an invaluable tool to organize scattered ideas. Free to download and use. http://strlen.com/treesheets/

FreeMind – If you lean more toward the mind-mapping kind of program than the outline-type per se, then you might like this open-source offering for Windows, Mac, and Linux. The program uses mostly keyboard commands to create headings, sub-headings, and a hierarchical structure, in a mind-map format. Free to download and use. http://freemind.sourceforge.net/wiki/index.php/Main_Page

OpenOffice – For those who like using a word-processing program, but would rather not pay the Microsoft price, OpenOffice has plenty of features and a user-friendly interface that makes is a favorite among many. Free to download and use. https://www.openoffice.org/

FastPencil – Free to sign-up, online writing tool, project manager, and conversion tool that also offers distribution, editing, and marketing services for ebook authors. Some paid, some free, worth checking-out definitly. http://www.fastpencil.com/

Yarny.me – Free to use, online outline and writing application, offering features like search, tags, snippets, organization by tags/versions, note area, and a trash can feature that saves anything you delete, just in case you need it back. https://yarny.me/

Grammarly.com – While not necessarily writing software, Grammarly has some great perks of its own, particularly if you won't be hiring your own editor. Self-dubbed as “automated proofreader and personal grammar coach. Correct up to 10 times more mistakes than popular word processors.”
http://www.grammarly.com/

Mobipocket – With software for a Reader and a Content Creator for PDA and Smartphone users, Mobipocket has something to offer everyone. Distribute and sell ebooks, create personal content, or use the more advanced features.
http://www.mobipocket.com/en/DownloadSoft/default.asp?Language=EN
Kindle Tools & Resources https://kdp.amazon.com/help?topicId=A3IWA2TQYMZ5J6

Whiteboard – Lastly, this interesting online mind-mapping application is touch friendly for use on a computer, tablet, or smartphone. You can sketch, write, or share your information with others without downloading a thing. https://awwapp.com/

Although I have tried a few of these programs personally, I really haven't given them the kind of test-run that would allow me to share an opinion. Other than OpenOffice, which I use daily, I would say that there is always going to be a slight learning-curve with any new program. Give a few of them a try and let me know what you think.