Beyond Compare allows comparison of FTP sites, as well as comparing files. Very useful tool.
Pro Version, $70.
No sync.
SecureFX is a secure file transfer program, and the company also sells SecureCRT which is a professional terminal emulator whch may be useful for folks doing manual connections to radio gear. SecureFX supports file sync. This is a more professional grade package.
SecureFX $96
Bundle CRT and FX $206