solana/book/src/tictactoe.md

# Example app: Tic-Tac-Toe

[Click here to play
Tic-Tac-Toe](https://solana-example-tictactoe.herokuapp.com/) on the Solana
testnet. Open the link and wait for another player to join, or open the link
in a second browser tab to play against yourself. You will see that every
move a player makes stores a transaction on the ledger.


## Build and run Tic-Tac-Toe locally

First fetch the latest release of the example code:

```sh
$ git clone https://github.com/solana-labs/example-tictactoe.git
$ cd example-tictactoe
$ TAG=$(git describe --tags $(git rev-list --tags
--max-count=1))
$ git checkout $TAG
```

Next, follow the steps in the git repository's
[README](https://github.com/solana-labs/example-tictactoe/blob/master/README.md).


## Getting tokens to users

You may have noticed you interacted with the Solana cluster without first
needing to aquire tokens to pay transaction fees. Under the hood, the web
app creates a new ephemeral identity and sends a request to an off-chain
service for a signed transation authorizes a user to start a new game.
The service is called a *drone*. When the app sends the signed transaction
to the Solana cluster, the drone's tokens are spent to pay the transaction
fee and start the game. In a real world app, the drone might request the user
watch an ad or pass a CAPTCHA before signing over its tokens.