It changed everything on the Net. The power of Netscape Communications' Navigator software is remaking the entire information industry. Thanks to fast downloading and enhanced graphics, it's widely considered the best "browser" for surfing the World Wide Web. Available for free on the Net, Navigator now commands 70% of the Web browser market--far surpassing its predecessor, Mosaic, which was invented by Netscape co-founder Marc L. Andreessen. It's a tenuous lead, because nearly everyone, including Microsoft, is aiming at Netscape.