FreeMind
With FreeMind, you express an idea by creating a node; and you build up a "mind map" by creating nodes and child nodes, and joining these nodes together. You can expand and collapse these nodes for easy viewing.
One drawback of this mind map is that you can only create a new node by connecting it to an existing node or idea. So with a simple tool like FreeMind, you can't create a lot of random, orphan ideas and connect them up later.
ZuluPad or WikidPad
ZuluPad and WikidPad are a cross between a notepad and a wiki. They allow you to write text in a notepad-like interface and create wiki-like hyperlinks to other documents. When you click on a wiki link, that document is automatically created and displayed and you can view or edit it.
I use ZuluPad for its simplicity: there are no bells and whistles, such as the ability to embed images, in the free version.
One advantage of these tools is that you can link any idea to any other idea, or create orphan pages for ideas and link these up or relink them in some other way at any time. I find ZuluPad great for maintaining an easily-accessible record of facts about characters, locations, events and such like in my books.
• By Etienne de L'Amour ~ Google+