TCPFile is an Instant Messenger and File Sharing tool.

It is released under the GPL, the source code is here. It uses its own protocol. 

Main features: 

• All connections are direct, encrypted and zipped (except within a LAN). Very easy to set up.
  
• Highly configurable Interface, with presets from Hotkeys. Different Skins available (in the plugin)
• Plugin capability
• Usable as a Tunnel: Reroute traffic over tcpfile
• Easily transfer a file to a buddy, just drag it onto his Name or an IM Window
• Downloads can be resumed and can come from multiple sources
• Auto discovery in lan mode
  
• A folder with its full subfolders can be shared, either for certain buddies or publicly
  

TCPFile has been succesfully tested on following systems (with Sun vm 1.6 installed):

• Microsoft Windows XP SP2
• Microsoft Windows Vista & Vista SP1
  
• Ubuntu Gutsy (openjdk or sun VM)
  
• Gentoo (needs libgnucrypto-java package)
  
• Debian testing (lenny)

TCPFile works best on a 1.6 Sun VM.

However, since 0.3.2 a separate java 1.5 build is available, but it does not implement all features. The 1.6 build is highly recommended. 

Screenshot of version 0.3.3b under XP: 

Version 0.3.3b under XP