Scrum Study Cards - An easy to understand overview of the Scrum framework.
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.
Lavagna - OpenSource project management tool designed for small teams.
Planyway - Visual project management for Jira and Trello: manage resources, build project roadmaps, use time tracking.
Scrum for Trello - Adds functionality to Trello boards for your Scrum projects.
Wiplo - The easiest way to organize and run your business workflows.