I once recommended Skype for private communications, but as Edward Snowden revealed, after its acquisition by Microsoft, it was backdoored to enable electronic eavesdropping.
Since then, a Switzerland-based group that includes one of Skype's co-founders (Janus Friis) has created a new alternative called Wire that provides end-to-end encryption for voice, video, and text chat without advertising. Wire is available for Windows, Mac, iOS, and Android:
https://wire.com
My Wire user ID is "George Maschke."
Wire now supports the secure transfer of files up to 25 MB. So if you have any documents that you think AntiPolygraph.org should see, please free to send them to me via Wire.