GIF features retained in PNG include:

(courtesy of the FAQ maintained by Thomas Boutel)

Palette-mapped images of up to 256 colors.
Streamability: files can be read and written stricly serially, thus allowing the file format to be used as a communications protocol for on-the-fly generation and display of images.
Progressive display: a suitable prepared image file can be displayed as it is received over a communications link, yielding a low-resolution image very quickly with gradul improvement of detail thereafter.
Transparency: portions of the image can be marked as transparent, allowing the effect of a nonrectangular image area to be achieved.
Ancillary information: textual comments and other data can be stored within the image file.
Complete hardware and platform independence.
Effective, 100% lossless compression.

Important new features of PNG, not available in GIF, include:

Truecolor images of up to 48 pits per pixel.
Grayscale images of up to 16 bits per pixel.
Full alpha channel (general transparency masks).
Image gamma indication, allowing automatic brightness/contrast adjustment.
Reliable, straightforward detection of file corruption.
Faster initial presentation in progressive display mode.

PNG is intended to be:

Simple and portable: PNG should be widely implementable with reasonably small effort for developers.
Legally unencumbered: to the best of the knowledge of the PNG authors, no algorithms under legal challenge are used.
Well compressed: both palette-mapped and truecolor images are compressed as effectively as in any other widely used lossless format, and in most cases more effectively.
Interchangeable: any standard-conforming PNG decoder will read all conforming PNG files.
Flexible: the format allows for future extensions and private add-ons, without compromising interchangeability of basic PNG.
Robust: the design supports full file integrity checking as well as simple, quick detection of common transmission errors.

What all this means to someone creating web sites is that PNG is a vastly improved GIF-like format. It is supported in several browsers:

AIR Mosaic [SPRY] (Windows)
AMosaic (Amiga)
Arena [W3C] (Unix/X)
Enhanced Mosaic [Spyglass] (Windows, NT, Macintosh, Unix/X)
Mosaic 95 [Compuserve/SPRY] (Windows 95)
NCSA non-X Mosaic [NCSA Mosaic Team] (Windows, Macintosh)
NCSA X Mosaic [NCSA Mosaic Team] (Unix/X)
Netkit [Netsurfer] (NeXTStep/OpenStep)
Netsurfer [Netsurfer] (NeXTStep/OpenStep)
OmniWeb [Omni Development] (NeXTStep/OpenStep)
PNET [PNET Corp.] (Windows)
SPRY Mosaic [CompuServe/SPRY] (Windows, Windows 95)
WinCIM [CompuServe] (Windows)

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