Just like IRC is the little-known open alternative to the usual IM networks, the closest to Skype would probably be SIP (https://en.wikipedia.org/wiki/Session_Initiation_Protocol ), for which many clients are available: https://en.wikipedia.org/wiki/List_of_SIP_software

The article mentions 2 alternatives:

> I recommend http://zoom.us or http://appear.in as alternatives that don’t “help” you by exposing your contacts to the world.

zoom app on MacOS requires root permissions. No, thank you.

I don't think we can call landlines via these.

I have used Skype a lot for calling landlines and mobile phone numbers, in particular for people overseas where the phone bill would otherwise be high. I have also used this when I have zero phone reception but have access to Wifi.

I'm from Europe and I'm baffled that this would be a requirement for anyone these days. Are landlines still that common in the US?

I'm from Europe and I've occasionally used this feature when e.g. I'd lost my phone, but needed to make a call to a customer service department.

they are very commonly used for robocalls/junk calls