Have you tried Yammer.com?

 

http:/www.yammer.com

 

Use it for free if all your users have the same ‘domain’ on the end of their email. For example, if your entire office has teamexpansion.org email addresses, ask them to log onto Yammer and you’re in business! Instant Intranet! Learn more at the site. No charge as long as you don’t mind allowing things to be a bit “loosey-goosey” on administration. The network will be encrypted, mind you, so outsiders won’t be able to see or learn about your personnel nor about an of your sensitive fields. And along the way, you’ll pick up free calendaring, free discussion threading, free Facebook-like status updates, and much much more.