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.
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 reader, you can subscribe to the web address of your Recent Changes page — something like http://yourdomain.org/recent.