Countdown, chrono, game clocks and counters in one a page pure JS app for mobile and desktop, with an offline mode.
See http://allthatcounts.net/ for a working instance.
In "versus" mode, use CTRL to switch and SPACE to pause/resume if you don't want to use the buttons.
Code is under BSD licence.
To deploy : just copy / paste de code on your Web server root.
To dev, I advice you to use the provided dev server since it will prevent some headaches with browser security policies and it ignores the HTML5 app cache by default.
USAGE: python devserver.py [host] [port] [--with-cache]