The open source movement is, IMHO, a post capitalist phenomena, and could NEVER originate from a socialist economy, because open-ness and sharing which arises from individuals with open source, more or less SPONTANEOUSLY, is exactly opposite the state imposed sharing so characteristic of planned economies.
In a sense, state imposed sharing strangles spontaneous/open sharing by individuals in its crib, while capitalism creates the surplus and good will which allows skillfull and highly competent individuals to develop quality stuff and GIVE IT AWAY just for the heck of it, for personal satisfaction, respect amongst peers, or perhaps to set up a marketable name for themselves which will eventually lead to a higher paying job...
George Gilder in Wealth and Poverty is much closer to the mark where he shows that giving away the goods and providing a service to people is actually the pure essence of capitalism.
I'm gonna both agree and disagree with you. Certainly the open source phenomenon could never originate from a "Marxist-style" socialist economy, but it is identically the same as the "community" economy practiced in frontier days (think of barn-raisings). One gives of his efforts to others in hopes of gaining a similar contribution FROM others at some future time. I think you would be hard put to say that THAT "economic style" is "post-capitalist".