PumpKIN is an open-source fully functional free TFTP server and TFTP client.
ZIM Client provides remote client access to ZIM database and application servers.
Tkabber is an open source client for the Jabber instant messaging system.
rdesktop is an open source client for Windows Remote Desktop Services.
UrBackup is an easy-to-setup open source client/server backup system.
Arma2 DayZ: Epoch is an unofficial open source client and server mod.
Free, open source TFTP server and client.
Open Client is a programming interface allowing access to any data source.
FTPRush is a free FTP client that supports FXP, SFTP, TFTP, etc.
3CServer is a TFTP and FTP server and client from 3Com for Microsoft Windows.