Graphical user interface is essential to interact to Desktop. Experts use only terminals but everyone is not expert. GUI brings lot of features on table and increases efficiency of average user. GNU/Linux has got pool of open source user interfaces to use. One can easily download and install the ui and use it. Every new ui has something new to offer.
It is developed under GNU project. It a developed by many contributors, major contributor is Redhat. It is very elegant and simple to use, it has basic tools like text editior, shell, audio and video player etc.
It is most used ui. It is very user interactive, elegant,vast varities of tools and similar to windows layout. It's technology also runs on smartphones and tablets.
xfce is free open source project. It aims to be fast and light weight for system and visually appealing to users. It simplicity makes it very easy to use.
It is forked from famous GNOME2 ui and several applications were written from scratch for it. It is considered as new ui like others. It has got a very elegant look.
It is forked from GNOME3. It is very user friendly espically for the starters. It has custom ui with transition and transparency effects. It has got nice panels and extension in ui.