Direct connect is a peer-to-peer file-sharing protocol. Direct connect clients connect to a central hub and can download files directly from one another. Hubs feature a list of clients or users connected to them. Users can search for files and download them from other clients, as well as chat with other users. (from Wikipedia)
DC++ is a free and open-source, peer-to-peer file-sharing client that can be used to connect to the Direct Connect network or to the ADC protocol.
LinuxDC++ is a Linux port of the Direct Connect client DC++. Though it is primarily aimed at Linux, it has been shown to work on other Unix-based operating systems as well. It is written in C++ and makes use of GTK+ for the user-interface. LinuxDC++ is free and open source software licensed under the GPL.
ShakesPeer is a peer to peer (P2P) file sharing program. It is a client for the Direct Connect protocol. The main goal of ShakesPeer is to create a fully featured client, compatible with DC++, that runs on Mac OS X with a native Aqua GUI. The program is released as Open Source under the GPL License.