Bonus (not designed by me).
If a diary/epistolary/journaling kind of horror story sounds interesting, check out English Eerie:
It's played with a regular deck of cards and almost feels like a creative writing exercise, but it's very fun! It comes with 4 or 5 scenarios which give you an initial situation and prompts.
Which other solo games do you like?
BTW English Eerie is not "free", strictly speaking, it's Pay What You Want. But you can get it for free to try it out, and then throw some money at the author if you end up liking it.
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