The RingCentral for Desktop allows you to screen callers using the Screen Voice Mail Live feature. This comes in handy when you're expecting a particular call by sending everybody else to your voicemail.
To screen callers, click on
Screen Voicemail Live once you receive a call.

To interrupt a caller leaving a message, click
Pick Up. Otherwise, click
Stop Listening to end the call, but this will allow the caller to finish his message. You can then check the message at a later time under Voice messages.
See Also:
RingCentral desktop app: Pre-Call Controls