Recently I had a chance to play with webhooks when I was trying to move jenkins to EC2 for my friend and as part of it I moved his svn to assembla.com. I saw webhooks and I thought I can integrate commits into svn hosted by assembla.com to pivotaltracker.com tickets. It took just 1 hour to do it but it was fun, apparently there are post commit hooks that you can add in svn but this was much easier to do because assembla.com has a webhook concept https://helpdesk.assembla.com/customer/portal/articles/1607029-configuring-the-webhook-tool so all I need to do is find a pivotal api that would allow to post commit messages to it.
It seems Pivotal tracker already has this https://www.pivotaltracker.com/help/api/rest/v5#source_commits_post . The challenge was that assembla webhook doesnt allow you to pass any custom header where I can pass the X-TrackerToken header but after some api documentation trolling I found that you can pass the token in query string like
https://www.pivotaltracker.com/services/v5/source_commits?token=sdfsdfdsfdsfdsfdsf and I was done. After Configuring the integration the commit messages show up in pivotal story.