Ticketapp is a free event booking app design concept released by Check JCD that includes 12 ready-made screens.
Brutalism is an amazing free UI web kit released by the design team at AND CO and available for Sketch and Figma.
Brutalism: A free web kit for Sketch and Figma
Material Icons Library is a free set including more than 1000 icons recently released by the design team at Pixsellz.
Material Icons Library: 1000+ free vector icons
A free iPhone X UI kit for Sketch based on iOS11 provided in both light and dark versions. Built and released by Design+Code.
iOS 11 UI kit for iPhone X
A free set of iPhone and iPad vector mockups in flat style for wireframing and UI presentation released by KK UI Store.