A free app for Android, by WhiteMountain.

This free Android app gives you a stopwatch that is easy to use and quick, and it has a button in the middle of the screen. Plus, you can press to set the beginning and ending points of the count. Because the buttons are arranged in such a way, the phone is easier to use from an ergonomic point of view because you only need to use one hand to operate it. The program has a straightforward but visually appealing layout and design. Lastly, if you are feeling artsy, there is a selection of color options available to enhance the aesthetics further.