GroovyDB is an appliance made by GroovyChannel that provides "SQL Virtualization" technology. It will be offered as a hosted "Cloud" service too.
They recently added Web Push capabilities, so that any changes to the data are reflected in real time through a Web front-end. The Comet Server used by GroovyDB is Lightstreamer.
Their site hosts a live demo of news pushed in real-time from the GroovyDB.
The Lightstreamer Adapter code they developed is available for download.