LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...

Chatib - Chatib is an online chat room where you can meet and chat with new people, make them friends, or even data them online.

MyChat - Secure instant messenger for any network

Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.

BORGChat - BORGChat is a LAN messaging software program.

Chattusa - Chattusa is a social network website that provides a free chat service and lets you connect with people from the USA without any hassle.