Cryptocat is a discontinued open-source desktop application intended to allow encrypted online chatting available for Windows, OS X, and Linux.

[4] Cryptocat was created by Nadim Kobeissi and further developed along with a community of open source contributors and is published under the terms of the GPLv3 license, although it has since been discontinued.

[9] In February 2016, citing dissatisfaction with the project's current state after 19 months of non-maintenance, Kobeissi announced that he would be taking Cryptocat temporarily offline and discontinuing the development of its mobile application, pending a complete rewrite and relaunch of the software.

[11] The new desktop-centric approach allowed Cryptocat to benefit from stronger desktop integration, in a style similar to Pidgin.

In June 2013, Cryptocat was used by journalist Glenn Greenwald while in Hong Kong to meet NSA whistleblower Edward Snowden for the first time, after other encryption software failed to work.

It had received points for having communications encrypted in transit, having communications encrypted with keys the provider did not have access to (end-to-end encryption), making it possible for users to independently verify their correspondent's identities, having past communications secure if the keys were stolen (forward secrecy), having its code open to independent review (open-source), having its security designs well-documented, and having completed an independent security audit.

[18] Cryptocat uses a Double Ratchet Algorithm in order to obtain forward and future secrecy across messages, after a session is established using a four-way Elliptic-curve Diffie–Hellman handshake.

Cryptocat's goal is for its messages to obtain confidentiality, integrity, source authenticity, forward and future secrecy and indistinguishability even over a network controlled by an active attacker.

[1] In addition to the Cryptocat client's end-to-end encryption protocol, client-server communication is protected by TLS.