ithinki - A simple user feedback tool for start-ups
Product School - The global leader in product management training
Herald - Bridge the gap between customer problems and product teams
The Product Manifesto - Product Managers face the biggest challenges of our day, which is why our community needs a common set of product principles.
FeedBear - The smartest way to manage feedback from your customers
Intercom on Product Management - The ultimate resource for aspiring product managers