Pushover is a simple push notification service to instantly send alerts to Android and iOS devices.

OneSignal is a simple and smart service that send push notifications across all platforms. OneSignal features reliable delivery of millions of notifications, segmentation and targeting, automated delivery, localization, support for all major app development tools, and real time analytics.

Pushbullet makes it easy to push notifications to your smartphone and computer from the web. These notifications are smart too: if you receive a notification with a link, tapping on the notification will take you right to it!

Amazon Simple Notification Service is a flexible, and fast messaging service which is fully managed. SNS is a simple and cost-effective method to message both distributed services and human recipients.

Urlooker is a tool for monitoring changes on web pages. Just select a page area, and you'll receive notifications about changed content.

Control your phone remotely with Tasker and AutoRemote.

Cross-platform push notifications with Pushwoosh!

Pusher is an evented pub/sub platform that lets you push real-time messages to web, mobile and IoT applications.

Push notifications for websites.

ActionSprout is on a mission to make it easier for nonprofits to reach, engage, and connect with supporters on Facebook.