Both parties will need to have this application running (and listening) in order to chat. Simply agree on a mutual password and record your friend's listening port number and IP address, and you'll be chatting in no time! Somewhat Secure Chat is only for Windows. This easy to use application is free and open-source; feel free to improve and distribute this program!
Binary (.exe): Download
Required .NET framework 4.0 installer: Download
Source: GitHub Repo