Wagn provides a feed (RSS) of recently changed cards which you can subscribe to in web browsers and feed readers. There's also a feed of the results of any Search card.
Example
See Recent Changes, or Wagn blog entries.
How To
On Recent Changes, or any Search card, you'll see the feed icon in your web browser address bar — usually something like 
. Clicking on it will let you subscribe to the feed. If you use a separate feed readers, you can subscribe to the web address of your Recent Changes page — something like http://yourdomain.org/recent.
Tips
In Safari the feed icon looks like this: 
.