Prototyping any type of design (web/app/code) helps minimizing hassle in the next steps of the creation process.

WireKit, a set of free Photoshop shape layers, simplifies creating prototypes for iPhone apps.

iPhone PSD Prototype Kit - WireKit

It comes in 2 versions: solid (realistic) and stroke (sketchy) where each version includes 60+ elements.

The layers are very well organized + named and they are all consistent in size + how they look.

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