Hi Scott, the Chatter is currently not supported for Mx 7. We are planning an upgrade for the widget
David,
When you are looking at App Store widgets, you can click on the All Versions tab to see the version history. This history shows the release version. You may find this to be helpful when looking at widgets for compatibility in the future. See screen shot below for Chatter, which doesn't show a 7.x release for the widget.