Pushbullet - Pushbullet - Your devices working better together
Pushover - Real-time notifications on your Android, iPhone, iPad, and Desktop
QPush - QPush is a free service that lets you easily push text and links from PC to iPhone.
Gotify - a simple self-hosted server for sending and receiving messages
AirMore - AirMore is a cross-platform toolset that can help you manage any Android device wirelessly.
Amazon SNS - Fully managed pub/sub messaging for microservices, distributed systems, and serverless applications