Desktop (windows) tray application with nice popups

I need a windows desktop application (Win 7 and Win XP), and if possible I would like the application to be cross-platform (for Mac and Linux). I need the application to run in the tray, with a context menu (righ-click) to popup main window or activate other functions. In the background, I want the application to request a specific URL via HTTP every 30 seconds, and display the result in the popup if it is different from the previous one. Example, the URL returns "hello", the first request popups up a message with "hello", then for the next hour, the message does not change, so there is no other popups, then the message on the server changes to "hello-2", then within 30 seconds, the application popups up this new message. I need the application to be able to popup small nice windows (without any title bar), like a MSN messenger popup at the bottom right part of the screen, with animation slide-up + slide-down. This popup can be displayed for a few seconds, or until the user clicks on close. If there is a 2nd message arriving (or 3rd, or 4th, or ...), it should be displayed on top of the previous one. I would like the application to be cross-platform, so I think Java is the best programming language for that, but I am open to suggestions. Also, I need this simple application to be very, very, very nice (like iPhone apps, with shades and 3D looks). So, java swing might not be the best framework. I would like the application to be built with a visual editor. Maybe javafx would be a good solution. I am open to suggestions if you have a better idea.