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.
Corrello - Dashboards for agile teams using Trello
Scrum for Trello - Adds functionality to Trello boards for your Scrum projects.
Toby for Teams - Better bookmarks, now with collaboration baked in 🔖