Both sites let users submit links/discussions into individual user-run communities, other users can then up/down vote them, and then the best stuff goes on the front page.
There's also http://www.snapzu.com and http://hubski.com that are a lot more similar to Imzy than many of the ones you listed.
I've been using Snapzu http://snapzu.com.
It's been around for a few years, even longer than Imzy.



ImzyA list of spaces to migrate to in a post-Imzy world.Jun 10 at 2:02 PM