The uPNG lib is being reused in multiple apps now, would be nice to decide where to put it and make it globally available.

The LICENSE of the uPNG lib is not compatible with Zeal's public domain license. A public domain / Creative Commons Zero / Zero-Clause BSD licensed PNG library implementation must be used for the library to be eligible to be merged to the OS repo. This could be done by finding one that has a compatible license, or to delete the existing library file(s) and begin reverse engineering a compatible-license PNG library from scratch. A simpler choice may be to instead make the software requiring a non-public-domain library to be a 'third-party' application, like ported emulators, living in its own separate repository at the Organization-level that can be optionally git cloned into Zeal's src/Home/ folder.

Good catch, I'll see what I can do.