animated png animated gif animated raw ;)
8bit alpha channel only 100% transparent or 100% opaque
RGB or 24bit color pallet only 256 colors
example filesize: 211kb(168kb when optimized) example filesize: 75kb
supported by firefox, opera and chrome (with plugin) based browsers supported by all browsers and IE

 

Tools and Plugins to view modify and create apngs.
my suggestion: japng editor for making apngs and setting custom frame delays. Paint.NET + plugin for resizing rotating and other image manipulation (files must have *.apng extensions). opera or firefox for viewing

Source files for some of the images among other stuff

Page with all images at once if you dare doing that to your system

 

animated images:

http://fruchtalarm.square7.ch/pony/apng/twilight_running_small.png
http://fruchtalarm.square7.ch/pony/apng/derpy_c_3.png
http://fruchtalarm.square7.ch/pony/apng/derpy_sleeping_high_fps.png
http://fruchtalarm.square7.ch/pony/apng/filly_flutterfan_by_pokerface3699-d4amcuf.png
http://fruchtalarm.square7.ch/pony/apng/flick_animation_wip_by_mattyhex-d4l6vbq.png
http://fruchtalarm.square7.ch/pony/apng/rainboom.png
http://fruchtalarm.square7.ch/pony/apng/shed_mov.png
http://fruchtalarm.square7.ch/pony/apng/twilight_shuffling.png
http://fruchtalarm.square7.ch/pony/apng/applebloom_blink_once.png
http://fruchtalarm.square7.ch/pony/apng/derpy_c_1.png
http://fruchtalarm.square7.ch/pony/apng/twitch_a_twitch_by_mattyhex-d4llvst.png
http://fruchtalarm.square7.ch/pony/apng/animated_apple_bloom_by_draikjack-d4ue8wv.png
http://fruchtalarm.square7.ch/pony/apng/derpy_c_2.png
http://fruchtalarm.square7.ch/pony/apng/677.png
http://fruchtalarm.square7.ch/pony/apng/apng_test____by_battybovine-d4mdsua.png
http://fruchtalarm.square7.ch/pony/apng/4th_wall.png
http://fruchtalarm.square7.ch/pony/apng/rd_stereo.png
http://fruchtalarm.square7.ch/pony/apng/luna_high_fps.png
http://fruchtalarm.square7.ch/pony/apng/bigmac_emote.png

 

Things that are only possible with animated PNGs:

Multiple overlays with hover effect
 
 and most importantly the browsercheck: ;)