Phoenix Startup UI Kit is a versatile tool to kickstart a landing page. It cointans 110 ready to use HTML5 cards coming with Sketch and PSD resources. With Phoenix Startup UI Kit it's really easy and joyful to create landing pages.
CSS Mint is a lightweight (just 3KB gzipped) and fully-responsive open source UI kit built to ease up layout and structuring of your web application. Built on top of normalize.css, it handles cross browser inconsistencies and provides minimalistic CSS components to be used in your application.