Tølløse station in Denmark. Which is for the local train, as tracks 1 and 2 are for the regional trains. I assume the local train track was added later, and was next to track 1, so rather than naming it track 3 or 11 (as they sometimes do to highlight an "in between track"), they went for track 0.
There is a bunch of pictures here[0], and you can spot in some of them where it says "Spor 0". But I assume "track 0" isn't _that_ uncommon after all.
Which leads me to wonder whether a "track -1" exists anywhere.