Not a web browser, but a program that interfaces with browsers.
It would be able to:
Synch up bookmarks between IE, Netscape, Mozilla, Opera, etc.
Store bookmarks in a database, sort by category/aspects, and import and export them to HTML and other formats.
Allow a "default" brower per bookmark, or popup to ask the user which browser they want to use to view the site.
More on this idea of mine, my wife is yelling at me to go to bed. Seesh! I work 10am to 7pm, hardly get any time to myself, and now I cannot even type in my brilliant idea to document what I had thought of. I spent between 7:30 pm to 8:45 pm with my family, took a break to check email, post and read on IWETHEY, etc and now I cannot even do that!