Forum Moderators: phranque
These slash-a-likes became rather infamous on the net - they became incredibly popular (php-nuke being the most notorious), and some of them had a whole lot of security holes and followed rather poor programming practices. Fortunately, in most of them, security has gotten better.
Slash-a-likes I'd look into are: postnuke, xoops, and mambo siteserver, and it lately seems like Xaraya is becoming less obscure - all of these will probably run on shared hosting with php and mysql (what you'll probably be getting). If you're not a newbie, and have got a dedicated server, you can try drupal, it's got a neat sort of blogging thing built in so people can have their own blogs.
None of these will really look like about.com out-of-the-box, but they will all give you a site out-of-the box with a whole lot of advanced organizational possibilities. And with just a tiny bit of php hacking you'll be able to get them into the exact format you want.