We use Slack for private projects. You can use this service in web browser or you can download an app for Windows or mobile. To register for an account visit: https://slack.com/. When you wish to connect you can click the social icon (#) on bottom of this website. You need an invitation to join our slack channel.
Public projects are available on Discord. This is a service for gamers but is also popular among programmers. To join this service you must register on Discord for an account and download the APP on your desktop. It also works on web-browser.
Slack Invitation: Join Slack
Discord Invitation: Join Discord