Zada is a Zlib implementation fully in Ada.
The advantage of Zada is its unconditional portability: native compiled code, but no need to worry about endianness or 32 bit or 64 bit versions, or bindings, or DLL's, or whatever.
So far, the project is dormant, but the realization is a straightforward task using two existing SourceForge projects:
1) Clone the ZLib-Ada thick binding project.
2) Replace the functions having Import pragma in Zlib.Thin (zlib-thin.ads) by native ones...