Does it exist any (free) zlib-compatible alternative out there ?

I understand that zlib archives can be decoded by any zip-compatible archiver. So there are a lot of implementations using the same format.
I would expect, following the discussion on this board, that a lot of different speed/compression combinations can be compatible, using more or less complex parsing methodology.

So the question is : does it exist a *.dll out there which compress in a zlib-compatible format, but, if possible, more (and slower).

This seems for example the case with 7z, which produces better-than-average zip compression.
kzip seems an interesting step into this direction too, except there is no source nor any *.dll provided, so unusable.

Unfortunately, 7z *.dll format seems uncompatible with zlib1.dll.
The dream would be :
drop-in compatible format (just drop away zlib1.dll and use the new one), but this last part might be too much to ask for...