Product Resources List - The biggest list of free product management resources
Wootric - Wootric is software that allows apps and websites to take customer satisfaction surveys so that you can properly gauge the popularity and success of your app through the eyes of the people using it. Read more about Wootric.
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.
TinyNPS - Simple NPS feedback
Intercom on Product Management - The ultimate resource for aspiring product managers
Customerville - Net Promoter Scores on steriods