Bitbucket started as a Mercurial host. The (internal unverified Atlassian) mythos goes, that in the early days, both GitHub and Bitbucket were on equal MAU foo

Bitbucket started as a Mercurial host. The (internal unverified Atlassian) mythos goes, that in the early days, both GitHub and Bitbucket were on equal MAU footing, but as Git mindshare started to take over, the Bitbucket founder, a Mercurial fan, dragged their feet on adding Git support. This delay lost them the war.