Microsoft OneNote 2007 is the best program you’ve never heard of.

Let me give you a little history, then tell you about OneNote 2007.

Microsoft Outlook has a rudimentary “notes” feature for jotting little bits of information on scraps that visually resemble post-it notes. Outlook’s notes are capable of being sorted and searched but there’s something about them that just doesn’t feel right. I’ve never met anyone who used Outlook’s notes.

Microsoft OneNote 2003 was not a secret – over ten million copies were sold. OneNote was originally marketed as a program for recording handwritten notes entered on a Tablet PC; it had the potential to do more but it wasn’t included in any Microsoft Office suite and never got any subsequent marketing push.

OneNote 2007 is a significant upgrade of the prior version; it can be purchased for less than a hundred dollars and is included in the Student edition of the Microsoft Office 2007 suite. It has the potential to become an invaluable tool for many people; I’m putting it on my short list of programs that are worth spending money on.

OneNote 2007 is deceptively simple and it will evolve into a different tool for each person. It’s a challenge to summarize it.

Broadly, it’s a program for taking freeform notes, with an interface that I found immediately intuitive. If you’re organized, you can sort notes easily into visually appealing notebooks, sections, and pages. If you’re disorganized, you can throw information into a pile and find things later.

You can type notes into it (or handwrite them, if you have a tablet PC). There’s no “Save” button – all information is immediately saved. You can paste in text, or embed whole documents. You can paste in images, send Web pages to OneNote, or capture all or any part of the screen. You can embed audio and video.

You can track tasks and dates and assignments. You can build to-do lists and then export events to your Outlook calendar. Send e-mails to team members from within OneNote. Sync status flags to Outlook. Use the OneNote Mobile application (if you’ve got a Windows Mobile smartphone or Pocket PC) to display your to-dos and collect notes to sync back to your PC.

Multiple users can share a notebook, and work in it simultaneously, with the results being saved and synced to all the copies. You can even do this in real time, in a conference room, for example, with multiple users editing a page to build notes and lists ” and even use some new drawing tools. (OneNote has been significantly re-architected to support autosave and range locking within a file.) Disconnected users can edit pages, and their changes are automatically synced to other copies of the notebook when they reconnect to the network.

One of the central uses for many people will be gathering information to use in a finished project created in Word, Excel, or Powerpoint. OneNote offers many flexible ways to get information out of it and into the other programs.

That sounds overwhelming, but I found it extraordinarily easy to start using it. You don’t have to take my word for it; go to Microsoft’s OneNote page and click on Take an online test drive. In about three minutes you’ll have a functioning copy of every Microsoft Office 2007 program running in your browser. (Requires a Windows Live ID, installation of an ActiveX control, and filling out a form.) Open OneCare and see if you can think of ways it might be useful.

If you’re curious enough to take a closer look, you can download a trial version of the full program and use it for 30 days. If you decide to buy it, you can buy a boxed copy but you’ll only be required to enter the license key to keep using the program.

I’m making it part of my everyday experience of using a computer.

If you want more information, you can get a nice description of OneNote’s features in this review, and some additional highlights in this overview.

Check it out!