Acorn RISC OS

Although there are undoubtedly other image viewers available for the Archimedes, discovering them is tricky for those who are unacquainted with Acorn software sites. But at least one PNG-capable viewer exists:

Translator

Version 8.00, John Kortink. Conversion capabilities.

http://web.inter.nl.net/users/J.Kortink/indexsw.htm