repoze.bfg used to cater mainly to people from the Zope/Plone-world — less cruft than Zope 2, easier to understand than Zope 3, but the same underlying ideas and mechanisms: object traversal for URL mapping, ZCML for configuration, an aspect-oriented vibe etc.

Ian Bicking made some interesting remarks about BFG back in 2008: http://blog.ianbicking.org/2008/11/06/where-next-for-plone-d...