This may be a fairly complex job. I would like to have a Prayer Circle created as a Wordpress plugin. It has two important functions to it, and one very important underlying element. One is on the Administrator side in that they can download the plugin, and install it on their Wordpress 2.0 platform. They will actually have very little administration of the actual prayer circle at that point.
The other side is that of the user, of course, who can join the prayer circle through the websites employing the Prayer Circle Plugin. They can also post prayers through the prayer circle and see responses to their prayers, as they are posted. They will be notified of a response to their prayers as they are replied to. That last part may not be possible due to the next part.
Here's the difficult aspect: All the prayer circles are linked spread out through various web sites are linked. When someone joins they get an email. When someone posts a prayer request they get an email informing them of new prayers to pray for at the site where they signed up.
The prayers from all over the world are tied together via RSS or some other means. So, everyone is looking at the same prayer board when they're on the web site where they signed up..
It may be that this is standalone software with a Wordpress bridge, or plugin.