I have just uploaded the first release in the syslog-ng Open Source Edition 2.1 branch to our website. It is currently only available in source format at this location:
This release synchronizes the core of syslog-ng to the latest PE version and adds the SQL destination driver.
This is an alpha release and thus might be rough around the edges, but it basically only contains code already tested in the context of the Premium Edition. The SQL functionality requires a patched libdbi package, which is available at the same link. We're going to work on integrating all our libdbi related patches to the upstream package.
If you want to know how the SQL logging works, please see the Administrator's Guide or our latest white paper Collecting syslog messages into an SQL database with syslog-ng. The latter describes the Premium Edition, but it applies to the Open Source one equally well.