What is it?
http://lh6.ggpht.com/_UhZZyEVmtlg/S6ErcLtI23I/AAAAAAAAz30/PvNnVCx8Zkc/s800/Screen%20shot%202010-03-17%20at%208.13.56%20PM.png
Screenshot from: http://googleblog.blogspot.com/2010/03/25-million-people-have-gone-google.html
Cf. http://googlesystem.blogspot.com/2010/03/gmail-contextual-gadgets.html

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hebbet it's a screenshot of http://www.youtube.com/watch?v=ORHFwcRhgDY#t=1m20s. It looks like a GTD system, but I ignore if it has been developed by a third party (a trusted developer using the new APIs http://code.google.com/apis/gmail/docs/#gadgets) or by the Gmail team as a new labs feature.