If you want GRUB to remember your last choice add:

GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true

Sometimes you need to perform a network installation (i.e. when no USB or DVD drive is allowed to boot, but you can boot PXE). In case of FreeBSD you can use DNSMASQ to serve the DHCP that will assign the initial client address and configuration along with PXE boot image served over tFTP. At this point you will have bootloader running, so you can serve filesystem over NFS to obtain working environment and/or the installer..

• Create a directory that will hold the target filesystem over network. In my case that was

  /usr/local/tftp/FreeBSD

• Put OS/Installer files inside above directory

  cd /usr/local/tftp/FreeBSD
  wget http://(..)/file.iso
  7z x file.iso

• Edit /etc/exports to export the filesystem over NFS

  /usr/local/tftp/FreeBSD -ro -alldirs -network 192.168.0.0

• Install the dnsmasq

  pkg install dnsmasq

• Setup the /usr/local/etc/dnsmasq.conf

  enable-tftp
  tftp-root=/usr/local/tftp/FreeBSD
  
  dhcp-range=192.168.0.50,192.168.0.60,255.255.255.0,1h
  dhcp-boot=boot/pxeboot
  dhcp-option=option:router,
  dhcp-option=option:root-path,/usr/local/tftp/FreeBSD
  

• Restart services

  service nfsd onerestart
  service dnsmasq onerestart

• In case you get bootloader running but troubles with NFS make sure that mountd is running. Also you can see who is using the NFS shares with

  showmount -a

PXE Boot always use initial DHCP/tFTP to fetch configuration and bootloader, so the first stage is similar and should work with other Operating Systems and Bootloaders as well, the rest is up to bootloader itself..

In order to create OSX installer on USB memory drive you need to:

• Download the Mac OSX Yosemite installer from AppStore on you Mac.
• Create installation media from Terminal by executing following command (remember to adjust YOURUSBVOLUME value):
  
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/YOURUSBVOLUME --applicationpath /Applications/Install\ OS\ X\ Yosemite.app --nointeraction

• Boot target Mac from USB by pressing ALT/OPTION key while powering-on the computer.
• Remember to format target drive first with Disk Utility if you want to perform clean installation.