Trello is an online tool for managing projects and tasks. It allows users to organize their work using boards, lists, and cards. Boards contain lists for different stages of work. Cards represent individual tasks that can be customized with checklists, attachments, due dates, and more. Users can create personal boards and teams to organize their own work or collaborate with others on shared projects. Trello provides a simple, flexible way to stay organized and track progress on various initiatives and tasks.