“Had we known about Facebook and Twitter and Google back in ’92 or ’93, we would have built them into the browser,” Mr. Andreessen said, referring to Netscape. “This is an opportunity to go back and do it right.”

Like other browsers, RockMelt will be free, and like the popular open-source browser Firefox, it plans to make money by earning a share of the revenue from Web searches conducted by its users.

For all its modern features, the challenges facing RockMelt, which is inviting users to try a test version on Monday, are enormous. The browser market has become intensely competitive in recent years and is dominated by giants like Microsoft, Apple and Google, as well as Mozilla, which makes Firefox.

“Getting heard above the noise is going to be hard,” said David B. Yoffie, a professor at the Harvard Business School and the co-author of “Competing on Internet Time,” a book that chronicled the battle between Netscape and Microsoft.

Consider the fate of Chrome, the latest major competitor in the browser market, which Google introduced two years ago. Despite good reviews and being heavily promoted by Google  through ads and links on the company’s home page, the most visited page on the Web  Chrome has captured just 8 percent of the browser market, according to NetApplications, which tracks browser usage.

Even Microsoft, considered a laggard in innovation for much of the last decade, has revamped Internet Explorer in recent years and is expected to release a new and improved version soon. A test version of the product was downloaded 10 million times in just six weeks, Microsoft said.

“There is no reason to suggest that the momentum that we have seen in the past six weeks is going to slow,” said Ryan Gavin, senior director for Internet Explorer at Microsoft.