SocialSizes - Sketch templates for sharing images & videos on social media
The Y Combinator Database - The definitive database of YC companies with all the metrics
Invision - Prototyping and collaboration for design teams
Startup School - How to start a startup, by Y Combinator
Craftwork - A collection of User Interface resources made by Craftwork
Y Combinator Companies - Interactive list of all 1000+ YC companies