ScreenTray - A better way to capture, annotate and share screenshots
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.
KShare - The free and open source and cross platform screen sharing software
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.
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
Dropshelf - Dropshelf is a place to put things. Drag anything to the edge of the screen, and a shelf slides out.