I was going to mention APNG but honestly it's dead. The PNG Group itself decided not to embrace APNG in April 2007. The format's years old now and even if it we

I was going to mention APNG but honestly it's dead. The PNG Group itself decided not to embrace APNG in April 2007. The format's years old now and even if it were to make a comeback, it still faces all the same issues as WebP except without backing from a single major party. APNG's degraded support is possibly even worse for adoption. It has all the same issues as WebP (see the shim discussion above) bundled with the fact that people don't expect PNGs to move. People either (a) don't know it's broken (i.e. think the single frame means it's a static image) or (b) know it's broken and chide you for using PNG instead of GIF.