Microsoft has placed the source code for ESE, the Exchange database engine, in GitHub for all to see. My favorite bit is the ESEUTIL program, which brings back memories of when it was the thing to take a mailbox or public folder database offline for defragmentation to recover some disk space. In Exchange 4.0 times, I was happy to get 200 MB back. Now it's all different...
https://petri.com/microsoft-open-source-ese-database
