Once you assign a task to someone, they get a notification on Karo if they have the app. Otherwise, the app first sends them a chat on WhatsApp, and if that fails, a reminder via text message.

A to-do list app called Twos is approaching this problem differently. When you add a task, it can suggest actions that might be relevant.

The best to-do list apps available for iPhone and Android include Any.do, TickTick, Todoist, and Microsoft To Do.