I have discovered one of the coolest sites I've ever seen. It is an online encyclopedia called WikiPedia.
It is easy to spend hours reading its contents, drifting from one link to the next, as you explore its wealth of information.
WikiPedia has several unique features: the site is a Wiki, and is thus editable by anyone, enabling the widest possible collaborations. Second, the contents are licensed under the GNU FDL, to ensure it remains free (as in Freedom) to everyone in perpetuity.
All I can say is: go have a read! It is very addictive. I plan to start contributing some articles soon.