&gt; You go through the list, find every successful open source project, and try to explain why it doesn&#x27;t count.<p>Wrong, I explain why in each case, they&#x27;ve completely changed the market, they didn&#x27;t just come in and take over from a successful and dominant proprietary player.<p>&gt;Oracle was the big dominant proprietary player when Yahoo decided to risk going with MySQL<p>No, they weren&#x27;t.  Oracle was never big in web databases.  Ever heard of the LAMP stack?  There was never a &quot;LAOP&quot; stack.  Oracle was never used as part of a stack with Linux and Apache and Perl or PHP.  Oracle <i>was</i> used in a bunch of big-iron systems back then (and still are), but they were never a serious player in small webservers.  MySQL helped create that market.<p>This is something like claiming that Harley-Davidson took over part of the market owned by the Ford Model T truck.<p>&gt;Now think how many websites are running on WordPress. It pains me to say it (because the code quality is so bad), but that&#x27;s an example of successful open source project.<p>Which proprietary product did it out-compete?  That&#x27;s right, none.  WordPress created a whole new market.  It&#x27;s just like all my other successful FOSS examples.  It never successfully out-competed a dominant proprietary product.<p>&gt;Git is up there too.<p>git is probably about the <i>only</i> FOSS product, now that you mention it, that&#x27;s made any real inroads against proprietary products, and even here, not that much.  It&#x27;s used all over the place for FOSS development of course, but there was never a dominant proprietary product used for source control for FOSS development.  BitKeeper was the closest to it, and that was only used for a single project AFAIK (the kernel), and using a special gratis license.  FOSS development has always been done with FOSS VCSes: CVS, SVN, Mercurial, etc.  Now, git has made some inroads against ClearCase and Perforce in corporate software development (as have all the other ones: SVN, CVS, Hg, etc.), but usually only for new projects.  ClearCase has been very hard to dislodge in the companies where it&#x27;s been standardized on (even though it&#x27;s an absolutely <i>abysmal</i> version-control system that only succeeds in hindering progress).<p>&gt;So if you define the category narrowly enough<p>I&#x27;ve already stated my requirement.  Show me a good example of a FOSS product completely taking over for a highly successful and dominant proprietary one, instead of just creating a new market or expanding the market (while not displacing the proprietary product at all).  I don&#x27;t think you&#x27;ll be able to come up with a single one.