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NGUI for Unity - A Review | Dark Genesis | Dark Genesis
So much is in flux at the moment but NGUI is still recognised as one of the leaders in GUI technology for Unity. Within these pages the author aims to walk you through all the components of NGUI and leads to you building a full game using NGUI (certainly possible but not something I'd recommend personally). There is a good introduction to using each of NGUI's components and how they fit in with Unity's own system.