Once you start using a note-taking application, you cannot live without it. These tools are so much more convenient than text editors when you just want to take or retrieve a few notes: You do not have to worry about when and where to save files (this is handled by the application itself), you do not have to find and open files in order to see your notes (as you would have to do with a normal text editor), the application is smaller, launching and responding faster than a full-blown editor, and has very streamlined operations for searching and updating notes.

So far, I have been using jNotes (the name is a little confusing, as it is not written in Java, has nothing to do with Japan, and there are also several other programs with the same name). jNotes manages multiple notes using tabs. The only essential feature it lacks is Undo, which is quite strange as Undo functionality on Mac OS X is provided by the operating system and thus comes for free (even PerlPad has it).

Today, I switched to Notational Velocity. It does Undo, it has an auto-completing search box instead of tabs, encrypts everything with IDEA (Are you paranoid enough? It does make sense, actually, if you store passwords with it), supports System Services, and can come to the front on a single and configurable keystroke.

Both applications are freeware.