Brad Silverberg and Adam Bosworth have known one another for a long, long time, stretching back to the days of Borland Software in the mid-1980s. Now, more than two decades later, the two technology executives are working closely together on a stealthy consumer health startup called Keas, Inc.

Ignition Partners -- the Bellevue venture capital firm that Silverberg co-founded after leaving Microsoft -- invested an undisclosed amount in the San Francisco startup along with Atlas Venture last year. You wouldn't know it from Ignition's Web site, which makes no mention of Keas.

I only discovered the information after a tiny nugget appeared in a blog on The Wall Street Journal.

In an email to TechFlash, Silverberg confirmed the investment and his role on the board. But he declined to offer any more details on the startup, which was formed after Bosworth left his executive post at Google nearly two years ago.

At the time of Bosworth's departure, I wondered if he might be jumping back into the startup game. (He previously co-founded Redmond-based Crossgain, which is best known as the company that Microsoft tried to torpedo when it accused several of the employees of violating their non-compete agreements at the software giant.)

After some legal wrangling, Crossgain was sold to BEA in 2001. He later took a job leading Google's online health efforts.

When Bosworth left that job to pursue "new opportunities," I noted that Silverberg would be a natural partner.

"I think the world of Adam," Silverberg told me at the time.

There are some other big names helping out Keas, namely Salesforce.com Marc Benioff and journalist Esther Dyson who are serving as advisors.

So, what's Keas all about?

Bosworth's most recent blog post offers some clues.