I mistook what you meant by "viewer". :/
Panini is a viewer in the sense that it uses OpenGL to render an image with a known x*y degrees of view and project it however you want [within its projection style limits, at least]. This doesn't help one post a navigable image in a web page, but it does give you a fast, self-contained, locally-run viewer.
To have a full 360-degree, manipulatable view you don't need to do anything beyond handing it a high-res equirectangular image [or any image with FOV tags, for partial projections]. You can mess with the projection type, viewing angle, rotation, etc. at will.
It more or less acts as a lens simulator, and lets you save the image as a jpeg if you like what you see. I lack the skill to get TIFF output working, but the jpegs it puts out are still excellent.
Usage: drop an image with FOV tags on it [the output of Hugin will have these]. Mess with the view. Click save if you like it.