ChatSecure
ChatSecure is a messaging application for iOS which allows OTR and OMEMO encryption for the XMPP protocol. ChatSecure is free and open source software available under the GPL-3.0-or-later license.

ChatSecure has been used by international individuals and governments, businesses, and those spreading jihadi propaganda.

History 

ChatSecure was originally released in 2011 and was the first iOS application to support OTR messaging. In 2012 ChatSecure formed a partnership with The Guardian Project and the Gibberbot app was rebranded to "ChatSecure Android".
 
In late 2016, the Android branding partnership was ended, with ChatSecure Android becoming 'Zom', and ChatSecure iOS remaining as ChatSecure. ChatSecure iOS remains in active development and is unaffected by this change. Version 4.0 was released on January 17, 2017.

Reception

In November 2014, "ChatSecure + Orbot" received a perfect score on the Electronic Frontier Foundation's "Secure Messaging Scorecard"; the combination received points for having communications encrypted in transit, having communications encrypted with keys the provider doesn't have access to (end-to-end encryption), making it possible for users to independently verify their correspondents' identities, having past communications secure if the keys are stolen (forward secrecy), having the code open to independent review (open source), having the security designs well-documented, and having a recent independent security audit.

See also 
 Comparison of instant messaging clients
 List of free and open-source iOS applications

References

External links 
 

IOS software
Free software
Free mobile software
Free XMPP clients