FXP.One is a FTP/FXP networking API that simplifies the creation of clients. It supports FTP and FXP, CCSN, SSCN, SSL/TLS, and all the usual goodies.
GtkFxp is a FXP client for GTK. With it you transfer files from a host to another host without the files ever going through your own computer.
lundfxp includes a Site Manager, GUI based client, transfers files site to site with CPS calculation for Unix, MacOSX, and Win32 platforms
proFXP is a FXP (server-to-server FTP) client written in Perl. It features TAB completion, site management, idle timers, SOCKS support, active and passive mode, different listing modes and a very powerful "down-to-the protocol metal" 2-char-command command line interface, pleasing newbies and hardcore hackers alike.
SwiftFXP is a GTK based FXP Client, hopefully you will too think it works like FlashFXP.