Enhancement features take advantage of special user or device capabilities and need to be backed up by more traditional implementations of the same interaction.
Enhance designs, themes, templates and downloadable graphic elements on Dribbble
Adaptive web-design-chapter-1
Scaling User Interfaces: An Information-Processing Approach
History of Hypertext: Article by Jakob Nielsen
Website Enhancements and Web Design Services
Progressive Enhancement: What It Is and How to Use It in Web Design - DIGITECH Web Design
Making the Physical Environment Interactive
WebTV Usability Review
6 effective website enhancements
Digital Content – Yun Huang's Portfolio
The Role of Enhancement in Web Design
Human Computer Interaction Articles, Videos, Reports, and Training Courses
Best Practices for Progressive Enhancement in Web Design - Hongkiat