Markdown by DaringFireball - Text-to-HTML conversion tool/syntax for web writers, by John Gruber
LibreOffice - Writer - Open-source cross-platform word processor.
GitHub Flavored Markdown - GitHub uses "GitHub Flavored Markdown," or GFM, across the site--in issues, comments, and...
Microsoft Word - Microsoft Word is a commercial word document processor for Windows.
Texy! - Texy! is a lightweight markup language as well as converter of this format to XHTML, in a form of a...
Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.