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I think pretty much the entirety of AWS would qualify. - https://plus.google.com/+RipRowan/posts/eVeouesvaVX

I have heard from friends at Amazon that that is in large part an origin myth. This is hearsay, so take it fwiw.

In gaming: all of the idTech engines, the Unreal engine, and so forth.

Unix was an internal tool at Bell Labs, as was C.

Rails was pretty much just a framework over at 37signals before it spread.

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This happens a lot in software.