Micheal Hickerson, Associate Director of the Emerging Scholars Network, recently published OneManOffice: Backpack. In it, he describes why he thinks Backpack is great: 1) You can start using it for free. 2) It's easy to use. 3) Multi-user features make it a great intranet. 4) It's a simple way to make public web pages.
What makes Backpack so great, as opposed to say, oh, any of the other organizational tools out there?It’s free. Actually it’s free for your first 5 pages, but that’s very useful in and of itself. That’s how I got started - created a free account and set up a few pages. I used the free account for months before I upgraded. And the upgrades are not expensive. The lowest level upgrade is $7 per month. (All of 37signals’ products are based on monthly subscription rates.)
It’s easy. It’s very intuitive, and there’s really nothing to learn. There are certainly some tricks that you can pick up from the user forums, but you can start using Backpack out of the gate without any kind of learning curve.
Is there anything else you need to know other than it’s free and easy to use? There is one more cool feature that will make it very useful to anyone who has to share information with colleagues in other offices.Recently, Backpack added a multi-user feature, so that it can act like an intranet for files, notes, or other things you need to share. You can also make Backpack pages public, making it a very easy way to create simple webpages. Here’s a public copy of my reading list, so that you can see exactly how behind I am.

"Here’s a page that I created to help me keep track of books that I want to read...(iBackpack is a little snippet of code so that I can use Backpack on my iPhone - cool, eh?)"