* free,
* end-to-end encrypted
* text and voice chat
* with pictures and group chat and what have you,
* using the Signal/OpenWhisper protocol,
* with desktop and web clients,
* open source (GPLv3, and on github [2]),
* signup with phone number or email,
* based in Switzerland,
* what else can you ask for?
Signal itself of course is pretty good, secure (recommended by Ed Snowden, famously), but not quite as fully featured it seems to me.
[1] https://wire.com
[2] https://github.com/wireapp
EDIT: added license, web client