A BBS or a newsgroup would fit the description of interactive, user-supplied content. These things are as old as networking. When the web came about, we immediately had chat rooms, web forums, blogs, and file-sharing sites. Again, they're as old as the web. I was a registered contributor to a predecessor to Wikipedia back in 1999.

Again, Web 2.0 is a mostly-meaningless buzz-phrase.

Facebook and Twitter are outrageously overrated.