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That specific one is done using Heap.  I've used Calq for previous games and that has worked fine to. Most web analytics tools have funnel support these days.

The big advantage with Heap and HTML-based games is that, after you've added their script to the page header, Heap automatically tracks all user interaction events on the page. In other words,  metrics instrumentation is requires a very small effort as long as your in game actions have unique link/button texts.