After Blogs, Wikis are probably the next most easy thing to get going in a classroom context. Actually they are often related. Certainly the are both online and both viewed (and edited) within a web browser (no word processor needed). A blog might document things learners are finding out - as individuals or a group. But the documentation is in a diary-like narrative form.
A Wiki, however, is a little more like the familiar way of documenting what you know. It is usually a little more like an encyclopedia. But the big difference is open access. Anyone can contribute, edit, add. Of course you may want to moderate this. But there are lots of ways of building structure around it. The starting point is a blank page, an index, and editor and all the linking and embedding that a web page allows you. Here's a video example (used also on our "e.g. wiki" section) to make things clear...