windows 7 - Storage disk format to use to be utilised by all OS

Aiming to have a large internal HDD to store files, and several OSes on separate disks. They all need to read and write to one storage drive.

Ubuntu (13.04+)
Mac OSX (10.8+)
Windows (7+)

What format should the drive be? Would like to avoid buying third party software, here's what I have discerned so far:

Answer

Generally I would now recommend to use exFAT; it's supported on the three major OSes and supports large files and a large number of files.

But if you want to use NTFS, you don't have to buy anything.* See How to copy files to read-only NTFS hard drive on a Mac – there are non-commercial programs to write NTFS on Macs. Just install ntfs-3g via Homebrew and follow the instructions that you're given on the command line. You'll also need osxfuse.

Then, you can use NTFS without problems, and also don't run into an issue with large files. With ntfs-3g, NTFS volumes will be mounted with read/write support, and in practice I've never experienced problems with it.

_{* There are commercial variants that promise better speed and support, like Tuxera and Paragon, but they are not strictly required.}