Can't really compare that to Skype or Discord, it's more like TeamSpeak (though better than that in many ways).
Well, as far as free and secure chat software goes: text chat -> host your own instance of free irc software (inspircd and countless others) or use trusted network of choice and connect with any free irc client, voice chat -> host your own instance of murmur or use trusted server of choice and connect with mumble. Combined that's probably all you need, unless you want a community gaming thing that's easy to set up and join like with a warlock discord (where security/privacy is probably not paramount anyway)
If you're looking for a free drop in replacement for skype, that's what tox is supposed to be although I can't vouch for that as I've never used it and the only thing I ever hear about it is that it's been a bumpy road as far as development goes.