Slack

Having to talk with people in the same company over email or to interact with multiple colleagues on the same subject can be a problem. This is where Slack becomes useful. It’s an application that aims to integrate a large number of services under the same roof.
 
The application provides real-time messaging across multiple devices, file transfer, file backup on most of the major services, integration with hundreds of apps, and of course instant synchronization across devices.
 
It’s also worth pointing out that Slack comes with various types of notifications, including for desktop, mobile, and email. Anyone can use the application for free, but there is also a paid plan that offers a number of benefits.