In Zoom, you can start a video call with one person and it will "ring" their computer with a pop up until they accept or decline. This will occur even if you already have one person in the meeting call.

In RingCentral, you can "ring" the first person, but to invite someone after that and still hold a video call with them, you have to give them a link, rather than calling them directly.

It also does not let you choose from a list of contacts inside RingCentral but forces you to use a phone number, email address, or copy/pasting link.