So, Wire (http://wire.com/) has started opening its server-side code:
https://github.com/wireapp/wire-server
They had already released a subset of the client code (same location as above) and have committed to releasing both client & server source code in full.
A review of Wire's security by @veorq and @marver can be found here: https://research.kudelskisecurity.com/2017/02/09/wire-cryptography-audit-with-x41-d-sec/
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