Software Product Management Stack - Resources & tools to help you manage your software product
Product School - The global leader in product management training
The Product Folks - A volunteer-led community of product managers and makers
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
The Product Management guide - A book on how to create and ship products that people love
Product Management Exercises - A repository of product manager job interview exercises