Simple Grid - Responsive & lightweight CSS grid for your website.
Anima App - Design, get feedback, convert to code, publish, iterate.
FLEX - An in-app debugging and exploration tool for iOS.
Sketch Repo - Collection of resources for anyone who uses Sketch
Flexbox Grid - Grid based on CSS3 flexbox
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.