I don't know whether it has been a while since you last used the SBB Mobile app, but it also offers the same functionality: start the trip by dragging a slider, stop it at the destination and the price is automatically calculated and charged from your card or invoiced at the end of the month. It works with the half-fare card, as well. Works all over Switzerland on trains, busses, cable cars etc. I haven't tried it with boats yet. :)

Like you say, a joy to use!