Take the intuitive simplicity of jotting down a quick note in Notepad, combine it with the ever-present nature of Stickies, and add easy linking between topics that's even more instant than TiddlyWiki. You've got Tomboy: a free application that makes managing your knowledge easy and fast.
Tomboy did not start its life as a Windows application: It is a part of the open source Gnome project, which is a desktop environment for Linux. To use it, you first need to install something called GTK# for .NET, a toolkit used to create cross-platform graphical user interfaces. This is a separate download, but the Tomboy installer links to it.
Once you have Tomboy installed, it looks like a native Windows application. If you are used to the tiny-looking notes that Stickies creates, you may be surprised to discover that in Tomboy, each note is a free-floating window that looks like a full application, complete with all the Windows chrome (minimize/restore/close buttons, toolbar, and so on). See all software downloads.
This also means that all notes are visible as individual windows when you hit Alt-Tab to switch applications, so you may not want to have many Tomboy notes open on your screen at any one time. Of course, you can always paste several notes into one big note, in which case you will have just one window.
Getting started with Tomboy couldn't be easier: Just start typing. Your text is automatically saved as you type; don't try to hit Ctrl-S to save your note. Counterintuitively (at least for Windows users), Ctrl-S triggers strikethrough formatting, so you'll need to wean yourself off any obsessive saving habit you may have unless you want all of your text to look like it's up for deletion.
Hotkeys are one of the few areas where Tomboy doesn't integrate so smoothly with Windows: You can specify system-wide hotkeys, but you do this by typing out their name (you literally have to spell it out, "+F3," angle brackets and all) rather than by hitting the keys you want to use like on most other hotkey-aware applications.
One of the most powerful features in Tomboy is inter-note linking. This is something Stickies can't do, and it turns Tomboy into a powerful knowledge management system a bit like TiddlyWiki. Often, you don't even have to think about creating links: Just type the name of an existing note and it automatically turns into a link, with no double square brackets or any other formatting.
If you ever rename the note you linked to, Tomboy will offer to rename all links to it, so there are never any broken links. It is also easy to create new notes by linking to them: Select some text and press Ctrl-L. The text you selected becomes a link, and you find yourself within the new note, ready to write. Tomboy stays true to the Wiki format by optionally supporting CamelCase: It can turn words melded together LikeThis into links.
Once you no longer need a note, just close its window and Tomboy will store it for future reference. If you ever need it again, you can click the Search button on any other note (or press Ctrl-Shift-F) and open the Search All Notes window. Type any fragment of text into the search box, and Tomboy searches all notes (both open and closed), as fast as you can type.