FileZilla is open source  FTP client and server software distributed free of charge under the terms of the GNU General Public License.
Features of FTP client:

Supports FTP, FTP over SSL/TLS (FTPS) and SSH File Transfer Protocol (SFTP)
Cross-platform. Runs on Windows, Linux, *BSD, Mac OS X and more
IPv6 support
HTTP/1.1, SOCKS5 and FTP-Proxy support
Network configuration wizard
Configurable transfer speed [...]

DC++ is an open source client for Windows for the Direct Connect network. Direct Connect allows you to share files over the Internet without restrictions or limits. The client is completely free of advertisements and has a nice, easy to use interface. Firewall and router support is integrated and it is easy and convenient to [...]