Talllly - A team to-do list that keeps score.
Taskful - Deadlines, meet your match.
ToDoBot - Slack-native todos right in your Home Tab
Streaks - The to-do list that helps you form good habits.
Today List - 24 hour to-do list, for Slack
ToDoBook - Turn your Facebook (& other social media) News feed into a to-do-list.