Kanban-style project boards from Atlassian. Still the simplest, most-loved task board for personal and small-team work.
From Wikipedia
Trello is a web-based, kanban-style list-making application developed by Atlassian. Created in 2011 by Fog Creek Software, it was spun out to form the basis of a separate company in New York City in 2014 and sold to Atlassian in January 2017.