BeeBEEP is a customizable chat and file/folder sharing tool for individuals or groups inside your local area network such as an office, home, or internet cafe. Conversations are peer-to-peer (no server required), encrypted, and messages sent to offline users will be delivered when they come online. Features include spellcheck, individual and group chats, sending screenshots and screen sharing.
Cross-platform with clients available for Linux, Mac and more.
May also function between machines on the same VPN service/connection.