For ages, it felt like the Linux world was settling for the appearances of GNOME 2 and KDE 3 but the individual projects behind these had other ideas. KDE has its pain first when version 4 was release but successive evolution appears to have mollified whatever complaints there might have. The release of GNOME Shell still continues to divide opinion though that too is maturing as part of GNOME 3.
The reaction to the dramatic changes made to GNOME resulted in two alternatives that are not dissimilar to GNOME 2 and both initially featured in Linux Mint. The first is a fork of GNOME 2 that is known as MATE (apparently pronounced “Ma-Tay” in spite of all appearances to an English speaker). That appeared first in Linux Mint 12 alongside a customised version of GNOME. With GNOME Shell still changing significantly every release, Linux Mint then replaced that option with Cinnamon. Though using modern underpinnings like GTK3 and eventually going it’s own way with them, it has much of the feel of GNOME 2 for those who fancy that more established feel. In fact, the GNOME project have since followed some of the lead of Linux Mint 12 by creating a Classic mode using extensions and you can experience that in CentOS or Red Hat Enterprise Linux, both of which are intended for the more conservative enterprise market.
LXDE is another desktop environment that keeps a lot of the feel of GNOME 2 and even uses GTK2 too. It is meant to be a more lightweight option that can be used on older computers and even has a variant based on Qt called LXQt in anticipation of a time when GTK2 libraries become obsolete. Staying on the lightweight theme, XFCE (pronounced “x-face”) is another good option that has a top panel and a dock at the screen bottom much like what you see in Mac OS X.
From the list that I have covered already, you should see that there is plenty of choice in the world of Free (as in liberty) Software. Linux has not kept all of its desktop environments to itself either with OpenIndiana using GNOME 2 and various BSD distros using a variety of desktop environments. Of the latter, PC-BSD probably offers the most choice with even GNOME Shell or Cinnamon on offer alongside the de facto default of MATE. So, UNIX operating systems get to benefit from the world of Linux Open Source software too so all can check out the list below to see what suits them.