Zoom video chat.
If you spend a lot of time doing video conferencing, there are quite a few options, but they all have limitations. For $10 a month, Zoom provides a combination of video chat (with 25 participants), remote desktop sharing and whiteboarding that are currently the best combination that I have found for consultants that need to both communicate and do software training. The only limitation is that it won't work in a technical support role as it suppresses UAC prompts entirely from remote view (a reasonable choice for compromising between usability and security). It does allow remote control of a participants PC (after authentication), but not remote administration.
For clients that are connecting using Zoom, the MSI installer can be found at https://www.zoom.us/client/latest/ZoomInstallerFull.msi