Meng Wong has a prototype project called Karma - so far I have found this page on it from July 2004.

I won't post the other URLs I found for Karma here in case they may have been indexed by mistake. You may find them by Googling for meng karma pobox.

2:28 Spam, SPF, DomainKeys, and Karma
by Meng Weng Wong - pobox.com
In the last two years a movement toward sender authentication has developed. It is now in full swing. Meng, author of SPF, will explain what's going on and talk briefly about Karma, the new reputation systems marketplace he's building.
Business