Pushover - Real-time notifications on your Android, iPhone, iPad, and Desktop
Pushbullet - Pushbullet - Your devices working better together
AirMore - AirMore is a cross-platform toolset that can help you manage any Android device wirelessly.
Gotify - a simple self-hosted server for sending and receiving messages
AirDroid - Access Android phone/tablet from computer remotely and securely. Manage SMS, files, photos and videos, WhatsApp, Line, WeChat and more on computer.
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.