PanoSalado is an open source Flash based viewer for cubic, equirectangular (spherical), cylindrical and QTVR panoramas.
It supports 2D & 3D hotspots, audio, video, and being extended via XML or directly via Actionscript (AS3). PanoSalado is based upon a (modified) Papervision3D core, and like Papervision is open source.
PanoSalado was begun in 2007 & formally announced in April of 2008. It was and continues to be a collaborative effort of Patrick Cheatham (Berkeley) and Zephyr Renner (Las Vegas).