PCBs are used for any electronic gadget, from your smartphone to industrial equipment such as electric drills. They can also be used by hobbyists who want to build their own electronics projects such as in the case of Arduino.
Singaporean software engineer Chai Jia Xun has recently used a PCB in an interesting manner. He created a palm-sized trinket prototype of the Singapore MRT, including the new Thomson-East Coast MRT line. Chai has been an employee at Silicon Valley for at least three years. As a graduate of the NUS School of Computing, he says that his education wasn't at all related to PCBs. However, his interest in train system maps and PCBs led him to create the prototype. He also revealed that he made the MRT prototype for the sole reason that it looks cool. Chai learned mostly from YouTube and used free software to start making his PCB projects.