Talllly - A team to-do list that keeps score.
Lunatask - All-in-one encrypted to-do list, habit and mood tracker, journaling and notes app
ToDoBot - Slack-native todos right in your Home Tab
The ToDon't List - A to-do list for avoiding the things you shouldn't be doing
Today List - 24 hour to-do list, for Slack
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.