What is the difference between GNOME, KDE, Xfce and LXDE?
- Unity is a nice 3D desktop environment designed for good performance on recent hardware. Unity is a graphical shell for the GNOME desktop environment. In 17.10 and later the Ubuntu Desktop uses GNOME as the default desktop environment instead of Unity.
- KDE is an alternative lighter weight desktop environment to Ubuntu's default interface. Plasma is the default desktop interface for KDE. It includes an application launcher (start menu), the desktop and the desktop panel (often referred to simply as the task bar).
- Xfce is a lightweight 2D desktop environment designed for better performance on older hardware.
- LXDE is a minimalistic desktop environment, somewhat like Windows XP in look and feel. It is designed to run on legacy hardware which requires a desktop environment that has minimal system requirements.
For screenshots and information about the comparative system requirements of different desktop environments refer to How do I find out which version and derivative of Ubuntu is right for my hardware in terms of minimal system requirements?.
Wikipedia has a comparison so you can look it up there. And the arch wiki has another too. Just read them through.
these are all desktop environments, you can still launch the same applications but how you get there and what they look like is a bit different. With some desktop environments you can change the appereance a lot (like KDE) while others will hardly allow you to change anything.
an other big difference is how much resources they will take from your system. If you have problems running Unity (default for Ubuntu) or KDE, XFCE or LXDE might run just fine.
As far as I know there is no connection between Gnome and the Mac OS.