The Darknet Messenger Briar just went into open beta status and it's working pretty well.
For communication Briar uses a peer-to-peer approach which sets him apart from messengers like whatsapp, telegram or threema. The connection to other users is established over the tor network, which is build into the app so you won't have to install a special tor app for this.
Also a very good feature is its possibility to work without an internet connection. It is just going to work fine over the same local wifi network or even bluetooth.
A main focus of briar is to reduce meta-data usage and of course every conversation is end-to-end encrypted.
At the end of the beta now created accounts will expire due to security reasons and incompatibility to the final version, but it's still worth giving it a try now.
https://briarproject.org/news/2017-beta-released-security-audit.html