Pramp for Product Managers - Practice product management mock interviews with other PMs
The Y Combinator Database - The definitive database of YC companies with all the metrics
The PM Interview - Practice PM Interview Questions (w/ timer).
Startup School - How to start a startup, by Y Combinator
Speechapp - The simplest way to practice for your next job interview
Y Combinator Companies - Interactive list of all 1000+ YC companies