Apply to YC (Y Combinator) - Curated collection of resources for founders applying to YC.
Startup School - How to start a startup, by Y Combinator
SuccessRate - You are welcome to submit your draft application before a deadline to get alumni feedback.
YC Interview Practice App - Get asked YC questions by Sam Altman
YC World - Explore Y Combinator companies by country
Reject Them Softly - Rejection letter inspirations from companies