FluffyChat - Open. Nonprofit. Cute ?
Softros LAN messenger - LAN messenger for an internal office chat for home or business users. It does not require a server and is very easy to install and use. It supports personal chats, group chats, message brodcasting, files transfer and remote desktop access.
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
MyChat - Secure instant messenger for any network
Molly (Signal fork) - Molly is an independent Signal fork for Android
BORGChat - BORGChat is a LAN messaging software program.