Invision - Prototyping and collaboration for design teams
Chipit - Store and tag all your screenshots.
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
Josh Parnham - Software Developer and organiser
Craftwork - A collection of User Interface resources made by Craftwork
Yoink - Yoink is a website that makes it easier to drag and drop images and text from one screen to another. It's a straightforward site with help along the way if you aren't sure about dragging and how to place your content.