Very very unlikely. A quick read of the
Wikipedia page shows that On2 has been highly protective of their codec, and while a couple of projects have put out decoders (and received flak from On2 for it), nobody has dared put out an encoder. If by some chance any do exist, they are illegal and buried deep underground.
Of course, now that Google has bought them out and released VP8 open source, there's a chance that it might see the light of day in the near future.