Nifty - Manage projects, work, and communications in one place.
Software Product Management Stack - Resources & tools to help you manage your software product
UnderPinned - One app to manage your projects from start to finish.
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 Management Exercises - A repository of product manager job interview exercises