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Gone - An ephemeral to-do list
tawk.to - tawk.to is a free live chat app that lets you monitor and chat with visitors on your website or from a free customizable page
Streaks - The to-do list that helps you form good habits.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.