Pushbullet - Pushbullet - Your devices working better together
Kingfisher - Organize and explain just about anything.
Pushover - Real-time notifications on your Android, iPhone, iPad, and Desktop
Explained Visually - An experiment in making hard ideas intuitive.
Gotify - a simple self-hosted server for sending and receiving messages
Crowdcast - CrowdCast provides webinars & virtual conferences.