Nifty - Manage projects, work, and communications in one place.
Intercom on Product Management - The ultimate resource for aspiring product managers
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.
Party Line - Use Slack to manage your projects
UpDiagram - Free agile project management tool for scrum team
Product School - The global leader in product management training