Bitcoin writes a new random number to its ledger every ~5–15 minutes. No one can predict or control it. Even = Heads. Odd = Tails.
Enter your name and choose how long to wait. You get a unique link.
Send it to the other person. They join and pick Heads or Tails.
You both type what's at stake and lock it in. Neither side can back out.
The next Bitcoin block arrives — a number the whole world sees at the same moment. Even = Heads. Odd = Tails. Permanent. Verifiable forever.