Release Notes: The first 5.3 release came out a few month ago. One of the main highlights was support for the Android platform. 5.3.21 is the second release. This is mainly a bugfix release, but it does include one feature which is potentially very interesting, support for Oracle JDK7.
Release Notes: Increased Performance: improved concurrency for multi-threaded applications on SMP systems. A new db_sql tool: automatic generation of Berkeley DB application code from SQL for faster development and migration. New APIs: support for C#/.NET and the C++ Standard Template Library (STL).