LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
Talk360 - Talk360 is a best-in-class communication utility that offers a convenient way to connect with loved ones globally.
Feem - Share files offline. No servers. No cloud. No limits.
aTalk - An encrypted instant messaging with video call and GPS features for android.
BeeBEEP - You can message and share files inside your intranet without a server.
FluffyChat - Open. Nonprofit. Cute ?