Two days ago I tried my hand at a more custom Ghost theme and I created Nyx, named after the Greek goddess of the night.
Nyx uses HTML5 Boilerplate for its core, snugly wrapped in Bootstrap and Masonry layers with just a hint of jQuery on the side.
All custom stylesheets are constructed in LESS and compressed to save precious bytes for mobile users.
As you can see, Nyx is very fast and light, Pingdom gave Nyx a Performance Grade of 100%.
It also has fantastic Page Speed and YSlow ratings thanks to GTmetrix
If you are interested in seeing more, head on over to the demo site for a live preview, or github for the free theme download.