Free Mockup Generator
Penpot - Design Freedom for Teams
Mokup Frames - Create Dribbble-ready GIFs in one click
Device Shots — Screenshot Device Mockup Generator
Mockup for iPhone 12 Pro Pacific Blue
Zeplin
Gravit
MockingBot - The Missing Prototyping Tool For Mobile
Wirify – The web as wireframes
Diagramly - Draw Diagrams Online
Frame Box - Lightweight online tool for creating mockups