Sacscha,
Our university has dump a lot of money into sakai. I don't know anything about it but I wonder if someone has compared sakai with zope?
I don't know Sakai either, but a 30 seconds look at http://sakaiproject.org makes me belive that you are compaing apples and oranges. Nowhere does that website say that Sakai is an application server - which is what Zope is.
Sakai is a tool supported by many academic institutions (generally of the University Level) to manage course, participants, teaches and resources required to support that [eg. assessment tools, collaboration tools]. As you say, it is -not- an application server and in fact runs inside a Java application server itself (its demo runs against tomcat but I'm led to believe any Java compliant servlet container will run it). A better question for David to answer might be: why do you want to compare Sakai with anything else, what is the actual reason for the question? If we know that, we might be able to find a comparable "apple" running on Zope, or for that matter using any of the various web-based frameworks that abound. DSL