Lubuntu and Xubuntu are both Linux ditros, and they are both based on Ubuntu. They are standalone distros, so they do not require you to install Ubuntu beforehand.

The great thing about these distros is that since they are both extremely lightweight, they will run on old or low-spec machines that would otherwise be rendered useless in today's world.

My personal favorite is Xubuntu, as it does not sacrifice eye candy to
the point of being ugly, while remaining blazing fast on older
machines. This is only my opinion, though.

Lubuntu is a fast and lightweight operating system developed by a community of Free and Open Source enthusiasts. The core of the system is based on Linux and Ubuntu .

Lubuntu uses the minimal desktop LXDE, and a selection of light applications. The focus is on speed and energy-efficiency. Because of this, Lubuntu has very low hardware requirements.

Minimum system requirements:

- 128MB of RAM (will give a slow yet usable system with a standard Lubuntu install)

Xubuntu is a community developed, Ubuntu-based Linux operating system.

Xubuntu is an elegant and easy-to-use operating system. Xubuntu comes with Xfce, which is a stable, light and configurable desktop environment.

Xubuntu is perfect for those who want the most out of their desktops, laptops and netbooks with a modern look and enough features for efficient, daily usage. It works well on older hardware too.

Minimum system requirements:

- 512MB of RAM recommended, 256MB minimum

- 4.4GB of free disk for the Live CD, 2GB if using the Alternate Install CD