Everything.PM - 300+ resources & tools for PMs, sorted by votes
Product Resources List - The biggest list of free product management resources
PM Starter Pack - Practical guide on how to get started in product management
Product Wednesday - Every Wednesday, receive a handpicked selection of tools made for Product Managers, Product Designers, UX Researchers and every member of the Product team.
Product Manager Handbook - Interviews w/ product managers + weekly newsletter
Intercom on Product Management - The ultimate resource for aspiring product managers