One of the best theme developers I know, Awshout/Anthony, has just released his new Framework for child theming, Reactor:
In his own words, earlier today, Anthony explained to me that he was trying to do something new:
I have looked through hybrid, startbox, canvas and some others. I’ll probably revisit some things (such as dynamic templates) as I get more feedback. I didn't want to just rewrite hybrid. Spine theme already took care of that angle http://paulwp.com/
If you just want to pick up a quick theme with a lot of administrative options, this isn't for you. Reactor is a framework similar to Justin Tadlock's Hybrid Core or 320Press, but based on the incredibly powerful Foundation 4 CSS framework from Zurb.
If you don't mind getting your hands dirty with CSS and WordPress hooks, this ranks up there with the best of the advanced frameworks.