Here is a nice a starter UI kit for Sketch for getting started with a movie booking apps designed and released by Kishore.
Freebies tagged: iPhone
Tourex is a free flight booking app design template designed in Sketch and Adobe Xd and released by Nasir Uddin.
A free Slack UI kit for iPhone released by Kevin Lanceplaine. It is basically a redesign concept that tries to solve some of the UX pain points.
A free set of isometric iPhone X Clay mockups released by Lstore to present your app design or create stunning dribbble shots.
A free iPhone X UI kit for Sketch based on iOS11 provided in both light and dark versions. Built and released by Design+Code.
A set of 8 free iPhone X mockups at 4k resolution available in PSD and Sketch file formats.
A free set of iPhone and iPad vector mockups in flat style for wireframing and UI presentation released by KK UI Store.
An early collection of free iPhone X and iPhone 8 mockups in PSD, Sketch, Ai and Xd file formats.
A minimal Apple iPhone 7 mockup for Sketch in two colours, White and Jet Black. Designed and released by Rifayet Uday.
A set of 9 3D iPhone mockups from multiple views and perspectives for showcasing mobile websites or apps. The freebie comes in PSD format at 4K resolution.