I remember CDF quite well. (It was developed, if I remember correctly, by a team based in Ireland with Europeans from several countries on board. I remember a presentation on it by a Norwegian working on the project.) It never took off and I was disappointed by the way it was launched as a commercial thing, we'll sell you a position...
Thanks for reminding me about it.
RSS, which I think is pretty analogous, was played better (though worse specified) and is now really widespread.
I'm not planning on going back to it, but I wonder if any browser still supports it. Anyone here know?
If it still works in some places, there's room to use it for some specialised purposes, like content that is deliberately limited to display on only some user agents.