Well, nowadays "Duden" is mainly a publisher's trademark, and lots of dictionaries and reference books are published under it.
But what Germans mean when they refer to "Der Duden" is the first volume of the series of Duden dictionaries,
Die deutsche Rechtschreibung (German Orthography), which indeed is a prescriptive dictionary, but only for spelling. It used to be the official, government-appointed standard for German orthography, but I don't think that applies anymore. There's a government commission now which discusses spelling rules and passes them on to the dictionary publishers.
The dictionary I quoted from, the
Universalwörterbuch, is too short to be compared to the OED; it's just a simple one-volume dictionary, perhaps like the Concise OED or Collins, Merriam-Webster, etc. I'd have to read the introduction to tell how prescriptive it is intended to be. I should suppose it's compiled from a corpus, but their definition of "Handwörterbuch" makes me doubt that a little.
AFAIK, we don't really have anything that can be compared to the OED in German. The
Deutsches Wörterbuch, started in 1852 by the Brothers Grimm of fairy tale fame, and finished in 1960, is the closest we have ever come. The problem of course being that it is seriously dated (especially the early volumes), but if you are looking for a strictly descriprive resource, with reference quotations just like in the OED, this is the place to go. It's actually online for free on a great website called
woerterbuchnetz.de.