Select Similar Layers - Sketch plugin to select layers with the same attributes
FlexboxPatterns - Build awesome user interfaces with CSS flexbox
Framer Inventory 3 for Sketch - Import states & export prototypes from Sketch to Framer
Webflow Flexbox UI Builder - Build flexible, responsive layouts — without writing code
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Fluid for Sketch - Sketch plugin to make your responsive designs more efficient