I have a Dell m3800 developer edition pre-installed with Ubuntu. I'm currently running 14.10. I am wondering if it is possible to triple boot Windows 10 and OS X Mavericks onto the computer?
Furthermore how would I go about downloading them and installing whilst making sure that grub isn't affected. Also I do not have any Ubuntu CD or install media
You could only do this, to my knowledge, if you had bought a Mac with OS X already on it or obtained a copy of the OS illegally as I am pretty sure Apple has copyright laws against purchasing the OS off of the machine. Someone please correct me if I am mistaking about this.
However yes, if you get a copy of any of these OSes and create either a bootable CD or USB, create a separate hard drive partition for each it should be possible for you to triple boot your computer. There are videos on how to do this if you do a quick youtube search though it sounded like your question was more trying to figure out if triple booting is possible and the answer is yes as long as you have enough space to partition. Just search for dual boot instead of triple boot cause that is what all the tutorials seem to do but it will be the same idea when you get to dual booting.
Like I said, Apple doesn't sell their OS outside of their machines so unless you download it illegally you can't download it but Windows does sell them. In fact, Windows 10 is still in development so that is free at the moment and available for download here http://windows.microsoft.com/en-us/windows/preview-iso
It is possible to install Windows, and that should be pretty easy, but your computer isn't compatible with Mac OS. I checked online and the only result I found for your computer was one saying it only boots into Safe Mode, which obviously isn't helpful. For Windows, though, get the Windows 10 Technical Preview ISO from Saige's link and burn it to a CD or a USB drive using UNetBootin. When you install WIndows, GRUB will break, but you should be able to get it as default again by using an Ubuntu LiveCD to chroot to your Ubuntu drive and reconfigure GRUB. You could also just use boot-repair which is provided as an ISO on the Ubuntu website. This should automate the process and get Ubuntu working as the default again.
There will be no problem with GRUB being overwritten by any other bootloader when you install all operating systems in UEFI mode, which is the default since computers ship with Windows 8. Just install every operating system as intended.
os-prober should be able to detect and include Windows and Mac OS in GRUB's menu, the answer to this question may be helpful: GRUB does not detect Windows
Further more downloading and installing Mac OS on a non-Mac systems looks very off-topic for this site to me and the same goes for instructions specific to a preview version of Windows that won't be available any more in a few weeks or months.
