http://www.netcaptor.com/

See SimulBrowse from SeaGlass Software.

Appears to be based on Microsoft Internet Explorer.

What happened to SimulBrowse?
Prior to version 5, NetCaptor was known as SimulBrowse. We changed
the name because, well, we didn't like it very much ;-)

SimulBrowse and NetCaptor share the same patent-pending browser
tab interface, but little else. They are actually written in different
languages and have completely separate code-bases. 
 

What's NetCaptor?
NetCaptor turns the browser world upside down. Unlike other browsers
which only view one site at a time or crowd multiple windows together,
NetCaptor opens sites on separate browser tabs. Take a tour.


NetCaptor for Mozilla
Many of you have asked whether we have a version of NetCaptor that
works with Netscape.
The answer is a resounding... SOON!

We plan to release NetCaptor for Netscape in late summer 1999.
Actually, most of the code is already done. We're just waiting for
the Mozilla Gecko rendering engine to stabilize before releasing the
product. 

If you are interested in being notified when the product becomes
available send us an email at netscape@netcaptor.com.