Lernit - Define objectives, assess and train your team
Product School - The global leader in product management training
Simple OKR - Track, measure and manage OKRs
The Product Manifesto - Product Managers face the biggest challenges of our day, which is why our community needs a common set of product principles.
FocusOKR - Focus and achieve your goals using Objectives and Key Results
Intercom on Product Management - The ultimate resource for aspiring product managers