I really like http://library.logos.com/?beta=true
It's fast. The desktop version uses "real" windows with columns, etc. But the speed is much different. Perhaps the only thing to be ported across the OSes is the Logos server engine. And everywhere, a browser could be used as an interface :-)
P.S.: Does anybody remember a browser-based Britannica Encyclopedia 1997 which worked in Netscape as if there were a web server running in Windows 95/98?