Zim is an open source WYSIWYG text editor for the Windows and Linux platform that takes word processing and note-taking to a new level by bringing the functionality of wiki to the desktop. If you create notes, to-do-list, or even write articles and you frequently need to switch back and forth between your notes, the proper way to organize is to create a wiki.
A desktop wiki is like a website with pages hyperlinked with each other, but instead of web pages you save your notes as regular text files. The main advantage of using a wiki like Zim is that you can create notes that can be cross linked with other notes or pages that you have created. Every page is saved as a plain text file with wiki markup. This means that you can create a note on Zim but later open it on any text editor. You can also link to external files or attach any file to page which can be anything from word documents to media files.
Linking pages is as easy as adding a hyperlink. If the hyperlinked page doesn’t exist yet, it’s automatically created and saved so that you can edit it later. Not only files are automatically created, they are organized in the proper hierarchy and directories are created and removed on the fly as you add or remove content in the wiki pages.
Zim handles several types of markup, like headings, bullet lists, bold, italic and highlighted. This markup is saved as wiki text so you can easily edit it with other editors.
Zim also has various plugins for that adds tools like Spell checking, Equation Editor, Calendar, a TODO etc.
Also see: Wikipad