Cinnamon was written from scratch to reflect a more traditional desktop metaphor. It was not created from existing GNOME code.

Many parts of Cinnamon were forked from Gnome 3 and Gnome 2 (Mate).

• XPlayer was forked from Gnome Videos (Totem)
• Xviewer was forked from Eye of Gnome
• Xreader was forked from Atril from MATE (itself a fork of Envince from Gnome 2)
• Xed is a fork of Pluma (itself a fork of Gedit 2)
• Cinnamon's compositor, Muffin, was forked from Gnome 3's Mutter compositor

Many other parts of Cinnamon are made from scratch, but it is not wrong the say it's also a Gnome 3 fork in many ways.