It's a shame they couldn't open source the original client and server software, would be interesting to preserve.
Conversations for Android is really good, and on iDevice ChatSecure works very well. Much better than what I expected. With filesharing and everthing. And then there's a bunch more that also work, but not of them at the same level of Quality.
Marketshare is super-low of course, but I like that it's possible to use an open protocol.
Decentralized, DHT-like, no phone numbers.
I've researched all others and Tox is the best choice ATM if you want YOUR data to belong to YOU.