I was recently introduced to Ning through a community project I'm involved with. Ning is a free on-line platform for blogging and social networking. It has all the blog posting features that you'll be familiar with but combines these with a membership facility. Members can communicate directly with each other through comments, or groups can be formed where discussions can be held. The basic platform is very flexible and you can easily introduce a number of widgets and features. There is also the option to pay for additional features such as hosting on your own domain name, removing the google ads etc.
What I like about Ning is that the discussion and interaction elements are to the fore-front - much more so than on a blog. I've been looking around for an on-line platform that is about more than just reporting and would lend itself to collective engagement and I'm quite impressed with Ning so far.
I decided to take a look and see whether unions had been picking up on Ning (there's a Ning search facility). Through that I came across UnionSocialMedia.org, a network for people who want their "union to make better use of new media and communications tools". I've joined up and you'll find a badge on the sidebar if you're interested. Thee is currently a really interesting discussion about the potential of twitter for union organising and activity.