Designed specifically to be played through the mail/post, AdventureByMail games have two players using regular playing cards as prompts as they write and send correspondences as spies, vampires, interstellar explorers, and more. However they do not draw prompts from their own deck. Instead, with each letter players send, they'll enclose a playing card to inspire their partner's reply. No GM needed.
Downloads includes a two-sided 8 1/2x11 trifold guide to play the game. Both you and your partner will need a copy of the rules (no need to purchase twice, just send the pdf to the other player), a six-sided die, a deck of regular playing cards, paper, postage, and envelopes.
If you're in the US, stamps can usually be purchased at a grocery store, just ask the person ringing you up. I'd also recommend buying cheap playing cards from a dollar store so you're not splitting up your good deck.
For a single player solo variant of any of these games, simply create the deck as instructed, follow direction for the opening entries and play as though keeping a journal as your character. You can add in additional cards for longer games if desired.