Zoomify was a popular viewer to display large images in the past with Flash (and now without it, of course). It is still used in various places, because it is not only a viewer, but a tile builder too and it has some enterprise features. Its popularity was related to the fact that an extension was added to a popular commercial image application. An old description of the format can be found here.
The tile sources can be produced by the commercial tool Zoomify, but scripts were written for common web languages (see creating zooming images). Other common viewers support this format, for example OpenLayers.
OpenSeadragon supports Zoomify tiles thanks to foobarable.
Currently, only inline configuration is supported, because Zoomify metadata are not in a standard xml file.
Supply all necessary information in the tilesource object. A minimal example object for this method looks like this:
OpenSeadragon({
...
tileSources: [{
//required
type: "zoomifytileservice",
width: 7026,
height: 9221,
tilesUrl: "/test/data/zoomify/",
//optional
tileSize: 256,
fileFormat: 'jpg'
}]
...
});