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.

Pusher Beams - Send push notifications programmatically at scale

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

PushOwl - Re-engage website visitors with push notifications

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

Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.