"Thwump" sounds happen in boxing matches, not offices. So when a loud thwump bounces off the exposed-wood ceiling in an office in San Francisco's once trendy south-of-Market district, every head turns. Programmer Jed Burgess is flat on his back next to a blue fitness ball. Burgess gets up, pulls his socks off for traction, and manages to balance atop the ball. Applause breaks out. Then the office returns to quiet discussions of software architecture punctuated by the clicking of keyboards. Welcome to Mitch Kapor's Open Source Applications Foundation.

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