LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
Dingtone - Dingtone is a free call and texting application for making unlimited calls and text messages to any number at the moment registered in any part of the world by any cellular company.
Feem - Share files offline. No servers. No cloud. No limits.
Textnow.com - It lets you text your friends, aka my only source of happiness
BeeBEEP - You can message and share files inside your intranet without a server.
FluffyChat - Open. Nonprofit. Cute ?