Posterous is a free, shared group blog. According to http://en.wikipedia.org/wiki/Posterous, it has been around since May 2009. I discovered it while researching Web 2.0 technologies to blog about. This one did take me a little while to understand and figure out to use. Don't let that discourage you, though. It's worth learning how to use!
You do not need to create an account to post something. All you need is an email address. From there, you can email audio files, movies, documents, pictures, links, comments, etc. to email@example.com. Posterous will email you back with the address to see your post. This is the only address you need to remember to post to your blog! You can even post things from your cell phone. However, since I will be using this with my students and text messaging rates are something I don't want to get involved in, I didn't explore this option. If you were using Posterous for personal use, this would be extremely convenient. There is even an i Phone app!
If you confirm your email address, you can customize your 1GB of space. You can make your blog site password protected, control comments, and add contributors, if you wish. You can control notifications for yourself and your contributors.
Their FAQ site is very informative and helpful.