They didn't release anything willingly. KHTML was LGPL so they were forced by the license to release it as open source. However the LGPL allows building apps on

They didn't release anything willingly. KHTML was LGPL so they were forced by the license to release it as open source. However the LGPL allows building apps on top of libs without releasing them as open source though and that's what apple did, they did not release Safari as open source, only webkit. So everything they could release as proprietary they did, they only open sourced the parts they were forced to. To be fair, they later rewrote KJS as JavaScriptCore and released it as open source using the BSD license, and also WebCore and more. See http://apple.com/opensource/ http://apple.com/opensource/ for more. By that time, many companies including Microsoft realized that releasing and contributing to open source was not only beneficial but also unavoidable.