Codegiant - Codegiant - Issue tracking, git repositories, continuous integration and documentation in a single platform.
Intercom on Product Management - The ultimate resource for aspiring product managers
GoRetro - a free retrospective tool for your Agile sprints
Product School - The global leader in product management training
Scrumpy - A simple, beautiful and agile project management software
The Product Management guide - A book on how to create and ship products that people love