Bootstrap has a very rich design already, so it's not a great scaffold to build on top of because there's very little room for you to add flavor and customization to it without making it look like a frankenstein design.
Skeleton is really minimal, it basically just does typography, some basic form styling, and a grid system. It's a much better base to work off of and add to than Bootstrap.
I love foundation it really does straddle the difference between bootstrap and skeleton, light and flexible while being fairly full featured. Plus the grid system is the tits.
Bootstrap has a very rich design already, so it's not a great scaffold to build on top of because there's very little room for you to add flavor and customization to it without making it look like a frankenstein design.
Skeleton is really minimal, it basically just does typography, some basic form styling, and a grid system. It's a much better base to work off of and add to than Bootstrap.