Nifty - Manage projects, work, and communications in one place.
The Product Management guide - A book on how to create and ship products that people love
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Product School - The global leader in product management training
Jira - The #1 software development tool used by agile teams. Jira Software is built for every member of your software team to plan, track, and release great software.
Product Management Exercises - A repository of product manager job interview exercises