"Popfly is the fun, easy way to build and share mashups, gadgets, Web pages, and applications. Popfly consists of two parts:

1. Popfly Creator is a set of online visual tools for building Web pages and mashups.
   
2. Popfly Space is an online community of creators where you can host, share, rate, comment and even remix creations from other Popfly users. "

It's all built using Silverlight so its a great little web experience - It kind of reminded me of a web version of iBloks.

Check out the Popfly Screencast for a quick 15 min overview.