Nifty - Manage projects, work, and communications in one place.
Scrum Study Cards - An easy to understand overview of the Scrum framework.
UpDiagram - Free agile project management tool for scrum team
Lavagna - OpenSource project management tool designed for small teams.
Hubstaff Tasks - Automated task management and time tracking
Scrum for Trello - Adds functionality to Trello boards for your Scrum projects.