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: