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Here is an interesting list of open source projects that use Vaadin.
Interesting because it has some entries from the Directory of Add-ons, but not all. Sadly, it's missing two I'm working: CKEditor for Vaadin, and Open eSignForms. Oh well, we take no offense!
I registered to suggest the ones I'm working (owlcms.googlecode.com and criteriacontainer.googlecode.com). We'll see if they picked them up.