SimWitty
A Security Information Management (Sim) system written in C# and available under the BSD license. SimWitty installs on Windows Server as a set of services and stores data on SQL Server. SQL Server also provides the data mining and SQL Server Reporting Services (SSRS) provides the reports. It integrates with network devices and *nix systems for holistic management.
Go to http://www.simwitty.org/
See also these related projects.