Nixie tubes have a lot of fans because of their retro style. They are neon valve tubes, where 10 cathodes shaped like numbers from 0 to 9 are switched on by plasma when high voltage flows through them. Patented in the 1930s by H.P. Boswau, they were wildly popular in the ‘60s and remained so until LEDs became cheaper to manufacture in the ‘70s. Many Makers today are creating vintage-look clocks using, now rare, Nixies bought on eBay with the help of an Arduino or Genuino Uno to control them.
In the video below, Jozsef Kovecses built a Nixie clock with NTP time syncronization using a Genuino Uno, a Geeetech IduinoShield, DS1307 RTC, DC-to-DC converter, and Nixie tube modules to drive the tubes directly.