Mosaic, originally developed by the National Center for SuperComputing Applications, was one of the first web "browsers" out there. It was originally developed for Windows, Macintosh, and the X-Windows system. Even though it was started in 1991, the developers canned the project in 1995 (with far superior commercial browsers out on the market, they completed their mission to make the web viewable. It is now open-source for people to view and to modify (if you qualify).
Mosaic was
not the
precursor to
Netscape (as some people think, as Netscape came "next") but rather Microsoft's Internet Explorer; Netscape was a
clean, developed from
main() codebase. Mosaic
spawned a
clone called
SpyGlass from which the
Internet Explorer codebase was originally started. In the Help...About
Microsoft Internet Explorer menu option in
IE5, Microsoft gives credit to the
NCSA at
UIUC, and specifically mentions Mosaic.
Mosaic is preserved for all of net history at:
http://www.ncsa.uiuc.edu/SDG/Software/Mosaic/