I imposed on [Jack] Real the requirement that he try to design the helicopter so that it could be serviced with six simple tools – any six of his choice. This was more a challenge than an arbitrary decision. I think most good designers want to keep things simple, but sometimes, for the sheer engineering delight of creating, things become unnecessarily complex and cumbersome.

Clarence L. “Kelly” Johnson Kelly: More than My Share of It All

Kelly Johnson was the head of Lockheed’s Skunk Works and a renowned aeronautical engineer. His Wikipedia article contains many more details, including his 14 Rules of Management.

Kelly: More than My Share of It All is also worth reading. It includes stories of Amelia Earhart, the SR-71 Blackbird and a 400lb lion chasing Althea Johnson (Kelly Johnson’s wife) around a factory.

I am not going to search for a software equivalent of “six simple tools” – that would be an analogy too far, and as Johnson goes on to say, the “six tools” are less of a requirement than they are about setting up an attitude. Maintenance matters. Simplicity matters. What use is the best helicopter in the world if you can’t keep it running?

I think there is a software parallel in this comment from Chris Jaynes (commenting on Tim Bray’s post On Duct Tape, itself a response to Joel Spolsky’s post The Duct Tape Programmer that in turn was inspired by a chapter in the book Coders at Work profiling Jamie Zawinski):

Yes, shipping version 1 is a feature, but shipping version 2 is ALSO a feature!

To that I would add:

Being able to fix bugs is a feature.
Being able to maintain code is a feature.
Being able to add features is itself a feature.