Puppy Linux 5.6 is an upgrade over Puppy Linux 5.5 "Slacko" and most notably it has full support for F2FS, the Samsung-developed "Flash-Friendly File-System" that was recently introduced into the mainline Linux kernel.
Phoronix benchmarks of Samsung's F2FS has shown great performance for all shorts of flash-based storage. With Puppy 5.6 is full F2FS file-system support, which was back-ported to its Linux 3.4 kernel.
Puppy Linux 5.6 also features improvements to its Woof build system, bug-fixes to the base packages, and many other package updates.
More details on Puppy Linux 5.6 can be found out from its release announcement.