AppImages are only for Linux based systems:

    https://appimage.org/

The AppImageKit AppImage can be downloaded from:

    https://github.com/AppImage/AppImageKit/releases


It is recommended to build AppImages on older distributions:

    https://docs.appimage.org/introduction/concepts.html#build-on-old-systems-run-on-newer-systems


At the time of this document, CentOS 6 is the one of the oldest supported Linux
distributions with the oldest libc version.

Use a custom configured PostgreSQL build with minimal options enabled to reduce
library dependency support.  Part of this reason is to make it easier to
include libraries with compatible licences.  Part of the reason is to be able
to build libpq with minimal development dependencies for PostgreSQL, since the
purpose is just to build a pg_top AppImage.

At the time of this document, PostgreSQL 9.4 was configured with the following
options:

    ./configure --without-ldap --without-readline --without-zlib --without-gssapi


Don't forget you may have to both PATH and LD_LIBRARY_PATH appropriately
depending on where the custom build of PostgreSQL is installed.