Fog Basic Features:
PXE boot environment (DHCP, iPXE, TFTP, fast HTTP download of big boot files like kernel and initrd)
Imaging of Windows (XP, Vista, 7, 8/8.1, 10), Linux and Mac OS X
Remote imaging based off of MAC address
Supports multi-boot pcs
Partitions, full disk, multiple disks, resizable, raw
Snapins to install software and run jobs/scripts on the clients
Printer management: deploy printers from web interface
Change hostname and join domain
Track user access on computers, automatic log off and shutdown on idle timeouts
Anti-Virus of network pcs
Restore deleted files
Bad blocks scan
Clonezilla Basic Features:
supported file systems GNU/Linux, MS windows, Intel-based Mac OS, FreeBSD, NetBSD, OpenBSD, Minix, VMWare ESX and Chrome OS/Chromium OS, no matter it's 32-bit (x86) or 64-bit (x86-64) OS.
Boot loader, including grub (version 1 and version 2) and syslinux, could be reinstalled.
Both MBR and GPT partition formats of hard drive are supported. Clonezilla live also can be booted on a BIOS or uEFI machine.
Unattended mode is supported. Almost all steps can be done via commands and options. You can also use a lot of boot parameters to customize your own imaging and cloning.
One image restoring to multiple local devices is supported.
Image could be encrypted. This is done with ecryptfs, a POSIX-compliant enterprise cryptographic stacked filesystem.
Multicast is supported in Clonezilla SE, which is suitable for massive clone. You can also remotely use it to save or restore a bunch of computers if PXE and Wake-on-LAN are supported in your clients.
The image file can be on local disk, ssh server, samba server, NFS server or WebDAV server.
Sources: https://wiki.fogproject.org/wiki/index.php?title=Introduction#Features ; http://clonezilla.org
Just trying to remain unbiased, both look to be excellent tools. Looking at the features of both and reading up on documentation on both of their websites it seems that clonezilla would be best suited for use in a work station type setup and that FOG would be better suited in an enterprise type environment complimenting the enterprise capabilities that Nethserver already offers.