Now Siddhi has become the runtime for WSO2 CEP server, and we have just released the WSO2 CEP 2.0 and Siddhi 2.0 comes bundled with it.
WSO2 CEP adds network support for Siddhi, and now you can use it with Thrift, HTTP, SOAP, and JMS. Siddhi/WSO2 CEP 2.0 has several cool (new) features, but let me briefly list few things I believe are the key.
1) Very fast (can do 1-2.5 Million events/ sec as a jar library)
2) Fast across the network too (about 0.25 million event/sec over thrift calls)
3) New Siddhi Query language (supports Filters, Windows, Pattern, Sequences, Joins). You can find the specification from http://docs.wso2.org/wiki/display/CEP200/Siddhi+Language+Specification
4) Supports Hazzlecast based highly available deployments and large working memories
5) Supports periodic snapshots of CEP state so it can recover the state in case of a failure
6) Integrate closely with WSO2 BAM. Basically you can setup a system where you collect data from many event sources and send them to both BAM and CEP using the same thrift transport so that the former can do batch style hadoop/hive based processing and the latter can do real time processing.
You can download the server from http://wso2.com/products/complex-event-processor.
If you are looking for Siddhi jar to be used with your java code, it is in the .zip file. Alternatively you can get the jar from http://dist.wso2.org/maven2/org/wso2/siddhi/siddhi-distribution/1.0.0-wso2v2/.
We have moved the code and mailing list to WSO2.
You can find the code from https://svn.wso2.org/repos/wso2/carbon/platform/branches/4.0.0/dependencies/commons/siddhi/1.0.0-wso2v3/.
You can find documents and samples from http://docs.wso2.org/wiki/display/CEP200/Complex+Event+Processor+Documentation.
Any questions, you can ask at http://stackoverflow.com/questions/tagged/wso2/.
I will soon write more about architecture and how some of the Siddhi/CEP features are implemented.