Trello is an web-based application, designed for group collaboration and project management. It organizes multiple projects into boards and at the same time you can see what’s being worked on, who’s working on what, and where something is in process. Trello was initially introduced by Fog Creek Software.
In Trello, boards represent projects and they contain lists — in other words, task lists. Each list contains cards, which correspond to tasks. The tasks or cards progress from one list to the next, using drag-and-drop. One example might be drafting the initial plan and going through the whole process until the implementation phase. Not only can users can be assigned to cards, but users, along with boards, can also be grouped into organizations.
(this is not an endorsement of the product or the developers)
Learn more from this descriptive video