I always find it a waste putting a 790MB Ubuntu iso on a 4GB DVD, and I was wondering how to put multiple operating systems on one DVD with a grub menu. I know it is possible, but I just don't know how!
I don't know if it can be done from within Ubuntu ( that I know of), but you can use MagicISO. The only problem it is Windows based. If you have access to a windows machine, it, you can take a look at it.
MagicISO has ability to create Multi-Bootable CD/DVD image file so that the user can incorporate multiple installation CD into one CD/DVD, and install multiple Operation System from one CD/DVD.1
Even though there's already an accepted answer i'll add this solution as well for the sake of completeness. And also coz' this answer better describes what's happening 'under the hood', so to speak. Creating Multi-Boot Discs.
May be you can use the Ubuntu AIO DVD, a collection of the most important Ubuntu 14.04 LTS flavors.
Made by Milan Rajcic and Nihil Enochian, Ubuntu AIO (All-in-One) DVD is an open source distribution of Linux which includes multiple editions of the world's most popular Ubuntu editions: Ubuntu, Kubuntu, Ubuntu GNOME, Xubuntu and Lubuntu in one AIO DVD.
Five Ubuntu releases on One Disk As mentioned, the distribution includes five different Ubuntu editions :
Ubuntu Kubuntu Ubuntu GNOME Xubuntu Lubuntu
You can download Ubuntu AIO DVD from SourceForge.
A program called multiCD can rebuild popular Distros to a bootable ISO with a GRUB menu, plus it works within Ubuntu.