Most people don't need an FTP program, but if you need one, I highly recommend this one. This free, program has many features that some commercial FTP programs lack.
FTP programs are used to transfer files across the internet. This is especially important for people with web pages who need to transfer files to the server housing their website. But this can also come in handy when it comes to transferring large files, especially files that are too big to email.
Version 2 only runs on Windows. Version 3, which is still being beta tested, will work with Linux and MacOSX.