The Networked City team use Slack. The key features are:
Slack is easy to use on mobile devices, and you can set up email notifications to alert you to conversations.
Sign in at https://networkedcity.slack.com/ if you have an invite, or email email@example.com for an invite for yourself or someone you recommend.
Choose something like firstnamelastname for your username so people can recognise you easily. Add a photo or other image to your profile.
Review the getting started checklist for some introductory videos
While you can use Slack through your web browser, it is better with desktop and mobile apps.
Here's what Slack looks like on the desktop
* Look through messages to get an idea of people's interests, then introduce yourself * Join any of the channels that interest you. You are automatically subscribed to #general * Check you have set up notifications to suit your preferences - details here * Get to know people!