It's both for planning /organising, and, if you want, for actually writing the novel.
From the site: "yWriter is a word processor which breaks your novel into chapters and scenes, helping you keep track of your work while leaving your mind free to create. It will not write your novel for you, suggest plot ideas or perform creative tasks of any kind. yWriter was designed by an author, not a salesman!
yWriter5 is free to download and use"
http://www.spacejock.com/yWriter5.html

And here's a thumbnail of a screencap:

:D