Web Based Collaboration Tools- 15! -All free!

This blog post has a really great range of web based tools that are all free with which you (and more importantly, your learners) can collaborate on-line, either in real time or asynchronously.  There are a few here that you have probably heard of (Google docs, Skype) and another whole load that you probably haven't (Twiddla, Wet Paint, VYew).  I have to confess that I haven't checked all of these out, but if you want learners to collaborate outside class, there are some very simple to use tools here, and they are all free.