The flexibility of Ubuntu (and Linux in general) means that it not very difficult to create derivatives from it – and there a number of derivatives. Ubuntu derivatives could be created for a specific function or created with different desktop environment. To receive support from Canonical, though, the derivative has to be officially recognized by them.Lubuntu is one such derivative.
In my last review I considered Kubuntu 11.04 as an alternative to Ubuntu for disgruntled Ubuntu users. But there's another Ubuntu derivative that should be taken into consideration as well: Lubuntu 11.04.
Lubuntu uses the LXDE desktop environment, a much simpler and faster alternative to Unity, GNOME and KDE.