I read it, I think, 5 years ago on what looked like the author's webpage, after following a link in a blog comment.
The story, as I recall it, goes like this. Three human space travelers are stranded on a deserted space station built by a very advanced civilization that, curiously, 'valued convincing others that they don't have free will over their own survival'.
To this end they built a couple of very fast computers that can somehow read minds but use that power solely for the purpose of convincing anyone in the vicinity that they don't have free will, e.g. by predicting their actions. Apparently the beings that built the computers have all been murdered long ago, but the computers are still there, and functional.
What makes the story interesting is the reactions of the three humans to the computer that are vastly different from each other and also evolve over time. In the end one of them even gets the computer to do something useful for them.
I quite liked the story and I hope someone recognizes it and tells me where to find it. I tried to search for earlier questions about free will on this site but could not find it.