You may access Esper source code including all regression test code and EsperIO source code from the Esper Github Repository.
You may access NEsper source code including all regression test code and NEsperIO source code from the NEsper Github Repository.
The most recent release is always in the "master" wherein our branches are used for current developmentand bug fixes.
Please ensure you adhere to the GPL license when using the source code.
The download page also offers source code excluding all test code for download.