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The lowly browser is becoming the most powerful piece of software on your computer. Despite the promises of chip makers and PC manufacturers, a Web application like Gmail running on a massive server farm thousands of miles away can often be faster and more reliable than the best client-based program.

Developers are pushing browsers to their limits by creating even better online alternatives to desktop apps, ranging from spreadsheets to instant messaging tools to full-blown operating systems.

However, storing your data remotely raises privacy and security concerns, and Web apps that rely on JavaScript are ripe targets for hackers. Browsers still struggle to mimic the interfaces of desktop programs, and no browser yet has an "application mode" that lets it appear on your desktop instead of as just another browser window among ten others.

Despite these limitations, innovative, agile, and low-cost Web services are blooming across the Internet's landscape. We looked at the best of the new Web services in 14 categories, ranging from online office suites and other productivity tools to recommendation services and event-listing sites. We found several knockouts, but we also identified a few sites that aren't quite ready to replace old standbys on your desktop.

Along the way we also found some of the best widgets--small desktop applications that pull data from Web sites--and mashups, which combine the best of two sites to make an even better result.