Hi, I'm a dev on Backstabbr and can help answer that question. Backstabbr was written in Python and is hosted on Google App Engine. The web interface uses Django and relies pretty heavily on Bootstrap 3. (At some point we'd like to migrate from Django to Jinja2, but that probably won't float to the top of our list anytime in the near future.)
Replying to you because you're the dev, just thought I'd let you know that your gravatar system is case sensitive, it seems to only work with all minuscules, yet google login seemed to automatically add capitals. So the combination means gravatars dont show up.
