VistA (the Veteran's Administration's health care) software was most decidedly a bazaar, not a cathedral. It was conceived by doctors in the late 1970s, and built either by health care providers or by programmers working closely (sometimes having chairs literally side by side) with health care providers. VistA is actually a loosely interconnected system containing over 100 integrated, patient-focused applications.
Distributed development started because many different doctors had bright ideas at about the same time. The distributed approach continued despite (perhaps even because of) overt persecution. When the developers tried to get together to formalize their relationships, they were discovered and disciplined (through firings or having their computers confiscated) because they were bucking the official mainframe-based IT team. The developers' tenuous position was reflected in the name they picked for themselves, the Hard Hats, and even more in the name attributed to them later by the head of the VA: the Underground Railroad.
Conceptually, VistA also emerged in a bazaar-like fashion. No one originally thought of the comprehensive life-long health management system VistA has become. Rather, each piece of the system emerged from a narrow need recognized by a health care provider: keeping track of diagnoses, analyzing diabetic nutrition, ensuring that medicine was administered to patients properly, and so on. Eventually, once the VA administration got on board the railroad, everything was linked together.
It's a truism that open source software development (and perhaps all software development ) is best driven by the people who will ultimately use it. So we can understand why VistA meets certain essential needs -- such as allowing an emergency room doctor enter an order within a few seconds -- that are missed by most proprietary software in the health care field. But I find it surprising that the system could work so well when each piece was developed in isolation. Perhaps the software used can provide a clue.