Greenshot - Greenshot is a free and open source screenshot tool that allows annotation and highlighting using the built-in image editor.

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.

Swiftdrop - Swiftdrop is a super simple cloud sharing app for Mac.

Dropzone - If you want your file uploads to work even without JavaScript, you can include an element with the class fallback that dropzone will remove if the browser is supported.

ScreenTray - A better way to capture, annotate and share screenshots

Dropshelf - Dropshelf is a place to put things. Drag anything to the edge of the screen, and a shelf slides out.