Adium is a free and open source instant messaging application for Mac OS X, written using Mac OS X's Cocoa API, released under the GNU GPL and developed by the Adium team. Based on the libpurple protocol library, Adium can connect you to any number of messaging accounts on any combination of supported messaging services (see further down for the list) and then chat with other people using those services. Note: They do not host any IM services themselves. Adium is a third-party client for connecting to services run by other people (mostly companies).
A new kind of instant messaging. Whether it's corporations or governments, digital surveillance today is widespread. Tox is easy-to-use software that connects you with friends and family without anyone else listening in. Tox is completely free and comes without advertising — forever
ZenChat is a highly secure messaging application that can be used as a standalone product or embedded within their Wallets. Users are able to communicate 1-on-1, through group messaging, or it can be set up for dedicated private channels