Now UI Kit - A beautiful Bootstrap 4 UI kit. Yours free.
UX Flow Wireframe Prototyping System - Create beautiful user flows prototypes for your next project
Dashboard UI Kit - A modern & responsive dashboard UI kit for designers.
draw.io - Online diagramming application
Landing UI Kit - Handcrafted UI components for landing pages
UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.