Designers still often create a specific user interface for every target platform they wish to support, which is timeconsuming and error-prone. The need for a multi-platform user interface design approach that designers feel comfortable with increases as people expect their applications and data to go where they go. We present Gummy, a multiplatform graphical user interface builder that can generate an initial design for a new platform by adapting and combining features of existing user interfaces created for the same application. Our approach makes it easy to target new platforms and keep all user interfaces consistent without requiring designers to considerably change their work practice. Categories and Subject Descriptors H.5.2 [Information interfaces and presentation]: User Interfaces