Flinto - The prototyping tool designers have been waiting for.
Product School - The global leader in product management training
Base UI Sketch Framework - Huge set of everything you need to design and prototype
The Product Manifesto - Product Managers face the biggest challenges of our day, which is why our community needs a common set of product principles.
Glyphy - Copy & paste fancy fonts + cool symbols ☞✺✐™
Intercom on Product Management - The ultimate resource for aspiring product managers