Class wikis

You can make a wiki of your own on the free site Wikispaces. Here's an example that I started, a family wiki. I constructed the main page and a page for myself, then sent invitations to my family members to join. My daughters rapidly constructed and edited several pages.

You could do the same for a class. The class wiki, if you don't pay for a higher-level account, would be visible to everyone, but you can make it so that only people you invite (e.g. class members) can edit pages -- that's how my family wiki is set up.

How to:

Go to Wikispaces and fill in the green box that says "Join Now -- Free!" You can make multiple spaces on your account, so go ahead and name one -- you could use the name of your class. The name has to be 3-32 characters, and can include only letters, numbers, and hyphens. You'll have to leave out spaces.
For your new space, choose the button that says "Protected (free)".
Now you've made a wiki space. Click on "edit this page" near the upper left.
Type in what you want to say on the main page of your space. There are tools in the bar above the edit space -- the drop-down menu box that says "normal" determines the text size. You can choose Header 1 for your main heading, for instance.
Highlight words in what you've written that you think might be good names for other pages in your wiki. For instance, if you've written a bit of course description, you've used some terms that probably could be expanded on. Highlight one, then click on the "link" icon in the edit bar.

You'll see this box:

Leave it as a Wiki Link, and be sure that the "new page name" is what you want to call it. In my Genetics wiki, I might want to have the word "expressed" link to the "expression" page, for instance, so I'd change that New Page Name on that menu. Of course, if you already have made a wiki page for the link, you'd use the drop-down menu to choose it. You could also link to an external site with the "external link" button.

Now click on the save button at the upper right. If you click on the new page link you made, you'll see a generic page, which you can edit to put in the appropriate content.