The simplest implementation only requires you to pass the text that you want to see in the window; it will automatically generate draggable window which users can minimize, maximize and close. It will have resizable borders and will be automatically centered on the screen. You can further customize it according to your needs using various options such as ability to specify height, width, enabling modal, and even pass external URL for content.
Developed by Michael Harris; PopIt Prototype script is available for download under MIT License. You can find further information, demo & download on PopIt Website.