This is the next level of the plain old link exchange. The basic principal is same - you advertise my blog, I advertise yours - but the way of implementing this is interesting. You pay for this advertising with Entrecard Credits, that you earn for free by networking (a.k.a. visiting blogs and dropping your card for other bloggers).

WeeWorld is a social network built for fun where you can meet and interact with WeeMees, invite friends, send messages, play games and create your own online cartoon page.