Several stimulating discussions with David D. Friedman helped me refine the `inverse commons' model of open-source cooperation. I am also indebted to Marshall van Alstyne for pointing out the conceptual importance of rivalrous information goods. Ray Ontko of the Indiana Group supplied helpful criticism. A good many people in audiences before whom I gave talks in the year leading up to June 1999 also helped; if you're one of those, you know who you are.

It's yet another testimony to the open-source model that this essay was substantially improved by email feedback I received within days after initial release. Lloyd Wood pointed out the importance of open-source software being `future-proof'. and Doug Dante reminded me of the `Free the Future' business model. A question from Adam Moorhouse led to the discussion of exclusion payoffs. Lionel Oliviera Gresse gave me a better name for one of the business models. Stephen Turnbull slapped me silly about careless handling of free-rider effects. Anthony Bailey and Warren Young corrected some facts in the Doom case study. Eric W. Sink contributed the insight that the factory model rewards shelfware.