This is a life points counter for Magic: The Gathering in under 350 bytes. It supports any number of players with changable names. See it in action!
<!DOCTYPE html><html lang=en><title>Counter</title><div><button onclick="document.querySelector('div').appendChild(document.importNode(document.querySelector('template').content, true))">Add Player</button></div><template><fieldset><legend contenteditable>Player Name</legend><input type=number value=20></fieldset></template></html>- The
<html>tag is optional, but I decided to use it to specify a document language. - This is meant as a joke. If you want to see a (slighty) more sophisticated attempt, check out kaunter.