Notepad++ for early stages and all the reference files* (Free). Runs on WINE fine.
A simple text editor on Android phone for notes.
Libre Office or Word 2002 for later stages after 1st Draft. Any version of Word after 2003 is madness to waste money on compared to Libre Office to give a Publisher a Word Document. Libre Office is gradually making it on to Android. But for serious writing a good screen and keyboard is needed. Phones, Tablets and Netbooks have neither.
Scrivener seems too proprietary and expensive.
lite version of Microsoft Word and other office apps are going to be downloadable in the Windows Store for Windows 10 at launch.
Yes, the first fix is free. MS since Vista and the evil Ribbon have lost the plot. I bought, sold, supported and installed their products for fifteen years. No longer. Bloatware, Adware and poor quality, too much concentrating on eye candy.
Windows 10 sounds like junk. Win8.x is mad. Win7 ought to have been free to Vista Users, it's purely a fixed version of Vista.
[* I also have a couple of mirrored copied of MediaWiki running that I paste background info, worldbuilding, research etc into, same SW as Wikipedia]