I had to use the so called "skype for entreprise". If you think skype went down, wait to try it, it's everything you ever dreaded, and more. It should be the example in wikipedia for the article "failure".

With the exploding number of chat apps, individual past, preferences and technical level I gave up on the whole rich client thing.

With all my customers I now use https://appear.in

It doesn't have great noise cancellation, the chat sucks and you can't send files.

But it works without any setup and little technical knowledge from my customers. They go to the address, click "accept" a bunch of times, and we see each others. We can even share screens.