APNG format is interesting: better than Gif (not limited to 256 colors, better compression) and simpler than MNG (that was bloated to be almost an video format).
But the designers of the PNG format detracted it as being a hijack of the PNG specification which was not designed to support animation and rather want adoption of MNG.
And the browser makers support neither APNG nor MNG (there was a brief native support in Firefox but it was removed), which make these formats less interesting, except for private use / limited share / intermediary format, perhaps.
HTML 5 and its native video support might be the final nail in their coffin...