Ubuntu MATE is a free and open-source Linux distribution and an official derivative of Ubuntu. Its main differentiation from Ubuntu is that it uses the MATE desktop environment as its default user interface, based on GNOME 2 which was used for Ubuntu versions prior to 11.04, instead of the Unity graphical shell that is the default user interface for the Ubuntu desktop.
Following up from Mint was MATE. Ubuntu MATE is essentially Ubuntu but replacing the Unity graphical interface with an environment called MATE (pronounced Mar-Tey apparently).
There has been some dispute since Canonical replaced the default desktop with Unity and MATE has become a popular alternative for users preferring the classic Ubuntu.
Late 2014, there was quite an excitement as a PPC version of Ubuntu MATE was announced and it has been well supported ever since, suggesting that this would be the best version to drop on the iBook.
It certainly ran well as a virtual machine and again came well packaged with the standard apps. It seemed that this was the ideal distribution because it felt the most complete version, even though with a clever, more lightweight, PPC foundation.