ZK is a slick-looking presentation layer toolkit that seems to at least be growing in popularity on SourceForge. I do not know of any real sites using it. It looked very interesting at first glance, especially in conjunction with something like Hibernate. After some further digging, my second impression is that it suffers from roughly the same major flaw that afflicted the first iteration of exhibition. Namely, it presented some simple ways to do complex things, but when it really came down to it, the complexity was merely being moved elsewhere. Not just that, but the complexity was now being exposed using a technology few people know or understand. Am I missing something here, or is ZK just refactoring the complexities of developing an application for the web?