If you've ever thought about writing a wiki, but wanted it for personal use only and didn't want to worry about hooking up to a server every time to update it, check out Zulupad. It's a program that runs off your computer, so you don't need to be online to use it. It has automatic hypertext linking, so if you reference something that you've already written about, it will automatically become a link. Looks like this could be a good program for a diary, or work items, or both. I've also used Evernote for the same kinds of things, and that program seems a bit more mature, but then again it doesn't have the automatic hypertext linking. Check them both out if this kind of program is what you need. They're both free.
Check out this page from Lifehacker on note taking tools and strategies to help you get the most out of this and other software.