Microsoft has been germinating a Complex Event Processing technology written by the SQL Server team for some time now.
The official announcement took place at Tech*Ed 2009, and an internal CTP has been floating around.
You can find the public bits (CTP2) available for download here as well as blogger Jesus Rodriguez's first thoughts here.
It also appears that MSDN has posted pre-release documentation here including Architecture images, sample scenarios, and documentation of the Microsoft.ComplexEventProcessing namespace.
I've pulled down the bits, set up a VM, and will be posting my notes shortly.
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