Big Free Clock is an application that displays a big digital clock on your desktop. Even though the default size is really big and uncomfortable, the size of the clock can be adjusted from the sides, selecting exactly the size you want. It even allows you to move the clock all over the desktop and select the position desired. By default, it displays a blue background with green numbers, but you can adjust the colors from the right click menu. What is more, you can even set the background to be transparent to view the desktop, make the numbers translucent and increase their size a bit. From the options menu you can apply a border to the clock, choose whether you want a 12h or 24h format, and hide the seconds. Unfortunately, it doesn't show the current date and doesn't include a calendar or alarms, which would definitely make it more complete and useful.
In short, Big Free Clock is a simple clock for your desktop, which doesn't have many options, but it is pretty customizable and free. There is no harm in trying it and see if it is useful for you.