Landing UI Kit - Handcrafted UI components for landing pages
Invision - Prototyping and collaboration for design teams
Now UI Kit - A beautiful Bootstrap 4 UI kit. Yours free.
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
Bots UI Kit - Fully customizable Sketch UI Kit for Messenger Platform
Craftwork - A collection of User Interface resources made by Craftwork