Well, it depends on what your product is. (I presume your story is about the product being useful.)

If it's your product, and it's a tech product, it might be appropriate for "Show HN". If you do, though, the tone should be "hey, you might find this interesting", rather than a sales job.

If the product solves a problem, you might find a Reddit sub about the problem.

Beyond that... I don't know.

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