Develop a Mac Application

I would like to create a little application that let the user make printscreen of his screen extremelly easily (just pushing a keyboard shortcut), make some annotations and share it easily. It's exactly like the app named LightShot ([login to view URL]), it install and imediately I can push command+shift+9 on Mac, select an area of the screen I want to make a printscreen, make some annotations (text, line, arrow or highlight something) and finally I choose what I want to do with the final image: 1- Choose to share it (generate a short URL) or 2- Copy the final image to my clipboard or 3- Save it on harddrive. The image must be uploaded into a third party storage like Windows Azure or Amazon S3 and the url must be of the web app will'll create to just get the image and generate the shortened URL. Initially the app will need to work on MacOS and Windows. The first version can be for MacOS and after we validated it, we can move it for Windows. Diagram: [login to view URL] In a second version we will create an account for the user into our webapp. Signing up into our web app he will can see images he shared, delete it etc Can you help me with that please?