Salza2 improves on the original Salza in many ways. The code's shorter, more readable, and has full documentation for library users. It achieves better compression ratios on all Lisps, and it's faster on (at least) SBCL and CLISP.
Salza2 is not backwards-compatible with Salza, but Salza's interface is so convoluted I consider that a feature, not a problem.
ZPNG is a slight improvement on Salza-PNG. The code has been somewhat reorganized. There's now some documentation. Since it uses Salza2, it generates smaller PNG files, faster.
Vecto has been updated to use ZPNG instead of Salza-PNG. Generated PNGs are smaller in general and very much smaller when an image has a lot of transparency.
I've been giving git a test run while developing this stuff, and there are public repos at git.xach.com. They include all the meandering commits of someone learning how to use git, so don't expect them to be particularly clean.