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https://riot.im has reached 1.0 and supports all the same features - except phones (Can be done with SIP integration).

Riot UI is (still) confusing for new users.

https://wire.com is also open source but much simpler.

But Wire is not a matrix client, is it?

If it is, they hide it well.

Correct, Wire is unrelated to Matrix/Riot. They were listing Wire as another option.