Join is an app that brings your Android device and PC together. Once you install it and set it up on your device, you can see all the notifications from your Android right on the screen of your computer.
The main difference between Join and Pushbullet -which is a similar app- is that join gives you the ability to interact with all the notifications of your smartphone, not just some. This means that you can answer a WhatsApp or text message, directly from your PC.
Other interesting features include the ability to share the content of the clipboard, and to write text on your Android remotely. You can also open browser windows, and view webpages on both your Android and your PC at the same time.
Join is one of those apps you don't know that you need until you try them. Apart from everything above, it lets you share files between devices, install apps remotely, find your lost Android, and much more.
