Some people aren't happy enough the usual old messaging apps. As you can understand, if your life depends on a secure communication, if you're a Russian spy living in London, or if you've just robbed a bank and you want to tell your mom, Snapchat is not the best option. You should go for a tool that guarantees the integrity of your communications and that can't be easily tracked by the bad guys, and for such purpose, you can use the TOR network and this CoyIM for macOS computers.
Once you've installed it, the first thing to do is configure your own account, proxies, and other technical issues. From that moment onward, you've only got to add your contacts and start the dialog, with end-to-end encryption and support for OTR and TLS.
The perfect alternative to TOR Messenger
Until now, those users with those needs could make use of Tor Messenger. However, since it has shut down, they're all searching like mad for a decent alternative and the creators of the TOR software have recommended CoyIM. So it can't be too bad. Furthermore, it's still under development so we should expect new functions sometime soon to improve its current features which are still very good.
One thing you should take into account is that its creators haven't yet carried out a security audit regarding their creation. Therefore, they recommend not to use CoyIM to transmit sensitive information until they manage to get it audited.