CEP Platform: C++ or Java
atomiclabs (via a colleague) has joined the CEP arena with an open source platform. Its curious that unlike Esper (Java/.NET), they have gone down the C++ road. The current closed source CEP products in the market space are split between Java implementations and C++ - as far as I’m aware not one of the leading CEP products is implemented in .NET. Esper managed to get “borrowed” by BEA (Event Server), hence it will be worth keeping an eye on atomiclabs (assuming they support more than MySQL).

url to atomiclabs has an extra “i” at the end
Although MySQL will initially be our only supported database, we’ll be adding all the other popular ones (Oracle, SQL Server, DB2, etc.) by the end of 2008.
BEA did not “borrowed” Esper for its event server but licensed it from EsperTech - see official news at http://www.espertech.com/news/20070717_bea.php
Otherwise, NEsper is a full .Net/C# version of Esper with same features and semantics.