Todoist is the task management app launched by Doist in 2007, serving 30M+ users worldwide. The free plan includes 5 private projects, and Pro at $5/user/month unlocks 300 projects with natural language quick add, making it the top cross-platform task management choice for individuals and small teams.
Pomotodo (Tomato Potato) is a Chinese Pomodoro Technique and to-do list app built around 25-minute focus and 5-minute breaks, syncing across iOS, Android, and Web with WeChat reminders for individual users.
Habitica is a gamified habit and to-do management platform from the United States with over 4 million users, turning habits, dailies and to-dos into an RPG leveling game that is free to use with an open-source core.