TClockEx

TClockEx is a lightweight application which gives you the possibility of tweaking some options regarding the time/date display of Windows.
Once installed, the app changes the format of the system clock. Thus, it shows the current date, day and time with seconds. Editing program options is possible through the Properties screen, via the context menu.
Therefore, you can create a custom-made clock display by choosing code elements; these focus on sample and default formats, along with date and time elements (e.g. week number, day of year, timezone name).
Other such elements involve system resources (e.g. show the available physical RAM or memory load), line positions and breaks, as well as hidden separators and literal text. But you can also build and apply user-defined elements.
In addition, TClockEx allows you to set the width of the clock display, establish the font, text and background color, customize the tooltip and copy-to-Clipboard format, as well as configure calendar settings when it comes to remembering its last position, making it stay on top of other frames, displaying week numbers, or highlighting specific days of the week.
Further features of the app revolve around mouse actions (single and double-button click) and menu options (e.g. fancy banner), while advanced users can tinker parameters in regard to the CPU and memory load. Plus, TClockEx can be set to automatically run at system startup.
TClockEx barely uses CPU and system memory, has a good response time to key strokes and mouse events, and includes user documentation. We have not come across any mishaps throughout our evaluation, since TClockEx did not hang, crash or display error notifications.
Its interface is outdated but that's because the utility has been overlooked for a long time. Users who are looking for customization features concerning the system clock would surely get a kick out of  TclockEx.