How can I create a "google docs like" structure on my site?

I am a med student. We have a lot of classes so I figured that we should collaborate to write our notes online so that we can have better quality notes.
I bought a domain name and a simple web hosting package with php and a mysql database.

This is what I would like to do:

I want to have one page for every single lesson we have, so for example i would have

example. com/microbiology/lesson_05_03_2012.html

or something like that. I want all the registered users of my website to be able to edit the contents of the notes, with a very simle online WYSIWYG editor, since not all of them are good with computers, this is why i don't want to use Mediawiki as a platform, it's not very easy to use, people get freaked out by codes, here I need everybody to collaborate.

Can anyone give me an idea on what platform to use? Drupal, Joomla, Wordpress, or something else. I can code HTML and Javascript pretty good, so I don't mind messing with code, I just need to know where to start looking...

Thanks in advance to all

Can you code PHP?

Hi
I don't know if Wordpress, Joomla have something like that. Most probably you need a custom made script created with a server side language, like PHP.
First, a script for register /login users, than the interface to add notes, and a table in database to store the records.
So, if you don't know PHP (or ASP.NET) you cannot create such website only with html and javascript.

This is actually my problem as well, I can hardly find out how to do Google docs like structure.. I hope somebody can help us..