Hunter TechLookup - Create lists of websites by technology for free
Startup Stash - A curated directory of 400 resources & tools for startups
Techmap.io - Techmap is a workplace search engine to find companies using technologies (e.g., Rails, PHP, Java, etc.) that are used internally. Finally, a "Google for Workplaces" that helps people find a place to work with technologies they love!
ProppyJS - Functional props composition for UI components (React & Vue)
xZeitgeist - The most popular tweets categorized and ranked, every day
Devhints - TL;DR for developer documentation