Adium
Adium is a free and open-source instant messaging application for MacOS. It has a built-in support for OTR encryption. It supports some of the popular messaging applications like AIM, Google Talk, XMPP, Windows Live Messenger, Twitter, and ICQ and allows users to chat with a lot of people on many different instant messaging platforms. Adium also has plug-ins for some other messaging clients like Skype, Steam, WhatsApp and Telegram but does not provide support for those. The application does not support video chat capabilities.