EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.

OneSignal - Customer engagement platform used by over 1 million developers and marketers; the fastest and most reliable way to send mobile and web push notifications, in-app messages, emails, and SMS.

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

SashiDo.io - SashiDo is the Parse Alternative for busy people.

Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.

SmartPush - SmartPush is a push notification service provider that helps businesses increase customer engagement using web push notifications.