Though this software is usable on standard Windows machines, it really is intended for use on Tablet PC's, that allow users to use their laptop's pen to write on screen. The tablet functionality of your laptop is what will really make this software sizzle!
At first glance, this software looks like a glorified note pad. However, you will quickly see that it's much more than that! Imagine that your notebook had limitless paper. Imagine that you could take long hand-written meeting notes, and then go back to search for your text later like you would in Microsoft Word? Even better, imagine that you could take your notes and convert them to text that you could share with colleagues. This software does all of that, and much more!
Microsoft OneNote is perfect for students, like myself. Users can take hand-written class/study notes, organize them, search through them, and even add images and annotations. In my classes, I have imported the professor's class notes into OneNote, so that I could put his notes beside mine and annotate as needed. Even better, you can use OneNote to record audio of your classes to play back later. Though, I'd recommend using a good quality microphone over your laptop's built-in mic.
I find Microsoft OneNote is very easy to use. The tabs allow you to quickly change note pads at the tap of the pen, for example switching from your Chemistry notes to your Math notes. Changing what you have written is easy! Either use the eraser function, or you can simply cross out what you have written and OneNote erases it automatically. Exporting your notes/audio to Microsoft Office or to your favourite email program to share with others is easy as well.
There are some other programs out there that do similar things, but I have not used many of them. Once I discovered OneNote, I didn't need to look any further. Of course, it may not be exactly what you are looking for, but I can tell you that it is one of the best programs I have seen so far. OneNote allows me to be 10 times more productive on my tablet PC than I was without it.