PNG (Portable Network Graphics) is an alternative for GIF format that was pattented by a company and abandoned by many designer and programmer because they have to pay a royalty to the company if they want to use GIF on their products or applications. GIF has one advantage over JPEG formats, which is GIF format can be used to produce animated images, instead of static images. For several times, many developers have tried to build a new format which can replace GIF as a standard, so here comes PNG, which was standarized by W3C along with their specifications. This format makes PNG was so popular, because it is small just like GIF and it also have advantages over GIF Format.
But, after the release, some people couldn't find the the animated pictures that was available in GIF Format. PNG can't do this, and some company, like Adobe still using GIF in their products, because many people still needs GIF in order to make their websites looks more interactive (and they will get more from Adobe's product license beyond the price that they have to pay for the GIF license).
But finally, the new format arrives, APNG (Animated PNG) is here. While it's still a draft, but many people will glad to hear this story. APNG is an extension of the PNG format, adding support for animated images. It is intended to be a replacement for simple animated images that have traditionally used the GIF format, while adding support for 24-bit images and 8-bit transparency. APNG is a simpler alternative to MNG, providing a spec suitable for the most common usage of animated images on the internet. APNG is backwards-compatible with PNG; any PNG decoder should be able to decode the first frame of an APNG and treat it as a normal single-frame PNG. However, APNG deviates from the PNG specification in a few minor ways.
I hope that this draft will soon approved by the W3C and become a new standard that extends PNG format.