As Joonas already explained, virtuallypreinstalled.com has been the playground for Vaadin apps since 2007. It was created to solve one of the most obvious blocker for good demo applications to exist: easy Java deployment environment. Everyone working at IT Mill (and few outside) to have an own place to deploy Vaadin apps.
Uilder, on the other hand, was something I personally needed for sharing/testing code snippets and samples, and I just leveraged the easiest deployment option for that. The uilder “branding” is just something wanted to test my creativity with 
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We are also working on to showcase demos (or production applications) better at vaadin.com. At some extent this should solve the fragmentation issue. Stay tuned for that.