Unity is the default desktop environment used in Ubuntu.
It is compatible with the GTK platform used by Gnome.
It was designed to be used for netbooks, but is developed by Canonical to be useful on all types of devices.
Warning: During installation from the Live CD, there is an option to install the boot loader to /dev/sda, which really installs the Grub2 boot loader to both the MBR (Master Boot Record) as well as the partition into which (K)Ubuntu will be installed.
Pay careful attention during this step if your system uses a boot partition, uses multiple OS (more than 2), or chainloads bootloaders.
For systems with such a boot partition, it is best NOT to overwrite the MBR.
In this case, the boot loader should only be installed to the partition in which the (K)Ubuntu OS itself will be installed.
(For example, if (K)Ubuntu will be installed to /dev/sda6, then only install the boot loader to /dev/sda6, not to /dev/sda.