It will work on any browser, but it's aimed at iphone/ipod touch.
It originated at this boardgame geek thread
There's 6 coloured buttons, in sort of standard game colours. Touch one, it gets highlighted and the timer at the top starts.
Touch it again, the timer stops and the button now shows the accumulated time.
Or -- touch another button, the first one updates and the second starts up.
New game just resets everything.
The app runs fine when the screen shuts off; everything just keeps going.
The clock stays running even when you exit the app (It's not really running; the start time is stored and retrieved on relaunch).