LiveView (iOS)
Used by 4 peopleapps.apple.com ↗
“When doing any sort of iOS work, I rely on an inexplicably free app called LiveView, which mirrors a part of your Mac's display to your iOS device.”
Neven Mrgan Interview, Designer (Panic Inc.) · via Uses This 
“LiveView iPhone app for quick and dirty prototypes and live visual design.”
Adam Glazier Interview, Interaction + sound designer (IDEO) · via Uses This
