Pushjet is described as 'Free open source push notifications' and is an app in the Development category. There are more than 25 alternatives to Pushjet for a variety of platforms, including Online / Web-based, Android, Windows, Android Tablet and iPhone. The best alternative is KDE Connect, which is both free and Open Source. Other great apps like Pushjet are Pushbullet (Freemium), AirDroid (Freemium), AirMore (Free) and Firebase (Freemium).
KDE Connect is a project that aims to communicate all your devices. For example, with KDE Connect you can receive your phone notifications on your computer, or just use your phone as a remote control for your desktop.