You can share your entire screen or a specific window with your Rainbow contacts. Sharing behaves like an audio/video call (WebRTC) during which you may activate a microphone or a video to converse with your contact.
This screen sharing is only available on your computer. Mobile apps (iOS, Android) can just receive the share, not launch it.

NOTE:
The installation of an extension is required to share a screen from Web applications.

How to Share My Screen?

To share your screen with another Rainbow user: 

• Go to the left panel "My conversations" to select one conversation or find the desired person in your "Contacts."
• Then, click on the icon "Share a screen or an application" located at the right of your contact's line.
• Choose between "Share your screen" and "With an Audio call"
• Select what parts of your screen to share with your contact and click on "Share" to start the call.
• You may "Add audio media" by clicking on the icon below your contact's avatar.
• To end the screen sharing, simply click on the red icon. 
• Information (duration, timestamp) about this call is then displayed at the end of your conversation wall. 
• You may (de)activate the audio and video at any time during your screen sharing activity. 

NOTE:
Your contact status will be affected by the screen sharing as it turns into "Busy" plus the indication "screen sharing" is added besides its presence.