StartupResources.io - Tightly curated lists of the best startup tools
INSTAD.IO - Automagically converts vector images into sketchy style
Startup Stash - A curated directory of 400 resources & tools for startups
Base UI Sketch Framework - Huge set of everything you need to design and prototype
Happy Startup Canvas - A simple framework for building stuff that matters
Sketch Extensions - An official collection of Sketch extensions & plugins