Markup is a framework for designing websites easily.
It has a plethora of useful tools — layouts, widgets, typography styles, etc. — to use as a starting point for your very own design.
Markup adheres to the latest HTML5/CSS3 standards and is search-engine friendly. Its layouts are responsive and the framework itself is fully documented.
While you might be tempted to stick to your old guns — jQuery UI components probably — Markup actually looks quite powerful and might be a refreshing change at least.