The EFF did a nice comparison chart on several messaging clients and how secure they are. I was surpised by a few had how limited they where. Some…not so much. Ones to look at in the future are listed below.
https://www.eff.org/secure-messaging-scorecard
SilentCircle (can cost money depending on options) https://silentcircle.com/
ChatSecure (opensource and support android/iOS) https://chatsecure.org/
WhisperSystems. (iOS and andriod, looks neat opensource t00) https://whispersystems.org/blog/signal