Repoze.bfg or Grok
BFG doesn't have very much to do with Zope, except:

it uses some Zope libraries internally.
it uses a variant of ZPT as its built-in templating language.
it uses some concepts, such as traversal, that will be familiar to Zope people.

If you know Zope 3 very well, and you like it, you'll like Grok.  If you want a framework maybe a bit more like Pylons, but slightly cleaner, and which uses some Zope technologies and concepts, you'll like BFG.
I am about to take the head long plunge into Zope land and am wondering which framework would fit my needs better. I have some experience toying around with django and the primary reason I am switching to a zope-based framework is ZPT and also needing to occasionally do things with Plone. Both seem to be well run projects I am mainly wondering which would have the better learning overlap with Plone? Thanks in advance!