I've found matrix[0] to work pretty well. Main downside is that the calls themselves are not end-to-end encrypted, but there is end-to-end encryption for the call setup. Riot[1] is available via f-droid[2]. You can host your own homeserver to prevent metadata leakage if you want, and run the TURN/STUN server to setup the calls if one of both parties are behind a NAT.

[0] http://matrix.org/

[1] http://riot.im

[2] https://f-droid.org/wiki/page/im.vector.alpha

How about wire? https://wire.com

So I had a flick through the website, and I fail to understand how this service makes any money.

This automatically makes me suspicious that either they'll eventually start collecting data, or the service will disappear as soon as they are acquired.

At least they explicitly promote with "No profiling or data gathering" with a link to https://twitter.com/wire/status/768797320792117248

Also they promote Spotify

I seem to recall that they aim for a freemium-ish model, i.e. sell extra features or charge for features designed for businesses/teams etc.

Looks great, I was not aware they had open source client.

Given that they were forced to release their Axolotl (aka Signal protocol) under GPLv3+, they try to add some strange restrictions [2]:

"Additionally, if you choose to build an Open Source App, certain restrictions apply, as follows: a. You agree not to change the way the Open Source App connects and interacts with our servers ..."

As I understand I am free to ignore any additions to GPL.

[1] https://medium.com/@wireapp/axolotl-and-proteus-788519b186a7... [2] https://github.com/wireapp/wire

I read it as that only applies when you connect to their servers, and is the usage policy/Terms of Service for their servers, not a code license.

I also recommend Wire. I tried multiple alternatives for Skype and Wire was the only one which had good call quality and clients for all major platforms.

Signal is available for desktop browser, although I don't know how well works.

Linphone is a decent alternative, it supports both voice and video calls.