On Friday, Apple seeded developers with Mac OS X 10.5.3 build 9D22. The latest build offers 15 new bug fixes to the latest version of Mac OS X Leopard. Apple has been aggressively seeded 10.5.3 seeds to developers. The previous seed (9d19) was released only 1 week earlier.
Once complete, the final Mac OS X 10.5.3 update will become available as a free update to existing Mac OS X 10.5 (Leopard) users via Software Update. No target date is set, but testing for a new version can extend over several months.