Code Kata
Code Kata is a programming exercise that helps software developers improve their coding skills through practice and repetition.
The term Kata comes from the Japanese culture, initially from martial arts. A Kata consists of a choreographed pattern of movements that are practiced, solo or in group, to achieve mastery of the movements.
Websites
There are many great websites that share tons of exercises, where software developers can practice their coding skills in a variety of programming languages.