Did you know that OS X, like any other Unix based operating system, comes with a build in FTP server called FTPD?
Unfortunately since the release of OS X Lion (10.7) Apple decided to remove it from the system preferences due to security reasons. However running your own local FTP server might come in handy to enable filetransfers between for example your scanner or security camera and your iMac or Macbook.
Now although Apple tried to hide FTPD for you from the GUI, its luckily still available though the command line.
In order to enable your very own FTP server you can open the terminal and type:
sudo -s launchctl load -w /System/Library/LaunchDaemons/ftp.plist
and to disable your FTP server type:
sudo -s launchctl unload -w /System/Library/LaunchDaemons/ftp.plist
However, a more user friendly and convenient way to manage your FTP server is by using a tiny free piece of software called Lion FTPD Enable. The current release (v1.3) is compatible with all versions of OS X including the latest El Capitan (10.11)