Many-jars started out several months ago as a full sized banner exchange. Initial joinings where promising and the exchange program i was using (3rd party) had an important feature, it allowed banners to be uploaded, a major sticking point with some websites on freeservers. The program was in a 'beta' mode but looked very nice.
To date the program hasn't credited one hit to the sites that have joined and I understand there are issues with IE6 displaying the banners. Several times a month I've had to 'bump' up everybody with free impressions and move the joining bonus up to match. I got to thinking that if i had to do all of that I should just do everything manually anyway and work on building and hosting my own exchange of sorts.
So with this in mind I was looking through my button exchange members, seeing what type of things they were using. One thing that kept catching my eye was the dropdown form exchanges using javascript. Luckily the source code for most of these was freely availible and I altered one a little to suit my needs. So I put it together, changed the join link on the many-jars banner exchange to point to new system.