If you can't beat 'em, join 'em. That's the idea behind Expresso, which offers an online service that lets users post and share Microsoft Excel files. Rather than reinvent the wheel, Expresso decided to set up its service around the world's most-used spreadsheet program. And more Office apps are on the way. --Andrew Conry-Murray

E-mail is a lousy way to collaborate on Excel spreadsheets. Expresso gets around that by letting customers post them on a secure online workspace, where they can invite others to collaborate. All it takes is a licensed copy of Office and an Expresso account. The software-as-a-service startup offers a free version and a corporate package at $79 per seat per year.

When a user uploads an Excel file to the company's service, it's loaded into an Oracle database. The spreadsheet owner controls access to the spreadsheet and can invite others to collaborate on it via e-mail. The owner controls edit privileges, such as who can read the file, make changes, or download it. Expresso allows control down to the cell level. The service maintains a detailed audit trail of every change made to the spreadsheet, including who made the change and when it happened.

Founder Nguyen comes from a company called SmartDB, which made software tools for the Oracle database. He sold SmartDB's IP to Rocket Software and used the proceeds to launch Expresso.

Expresso's use of Excel is a powerful differentiator versus Google Docs, Zoho, and other collaboration platforms, which offer alternatives to Office. Expresso plans to expand to Word and PowerPoint. The company was selected to join Microsoft's Startup Accelerator Program, in which Microsoft offers assistance to new companies. I'll wager Microsoft is interested because Expresso can keep Office customers from defecting to other systems while Microsoft develops its own SaaS offerings.