I can recommend Cobian Backup for this purpose. It's a general purpose backup software that can backup from/to a range of devices and protocols, including FTP, with the added capability of packing the backup into a ZIP file with a naming convention you chose. Its main features are:
- Backup to/from lone files, whole folders (including network shares) and FTP servers.
- Can schedule daily/weekly/monthly/yearly/periodic intervals for automatic backups, or manually triggered.
- Can do a plain file copy from source to target or pack the result into a .zip or .7z file, optionally with compression and password-protected encryption.
- Backup file names can be configured, being the date of the backup by default.
- Has full/differential/incremental backups, automatically deleting older copies and ciclying newer ones.
- Can run custom commands as pre-backup and post-backup events.
- Can use VSS service to backup locked files (although probably doesn't works for FTP sources)
On the bad side, the program lacks mainteinance (last version was released a few years ago). It's completely free but not open source (it used to be, and an older repository is still out there).