png22pnm.exe: Portable Windows (Win32) executable.
png22pnm.xstatic: Portable, statically linked Linux (i386) executable.
png22pnm.darwinc32: Portable, 32-bit macOS (10.5 or later) executable.
png22pnm.darwinc64: Portable, 64-bit macOS (10.5 or later) executable.
Source code is also available below.