A roulette game based on the Ethereum blockchain.
The game presumes you are using a web3 provider, I tested it with the Metamask plugin. It has no other backend besides the blockchain.
A main decision which had to be made, was how to provide the randomness needed to pick the winning number. I decided on using the hash number of a future block, although this is not a secure solution. Still I did not want to introduce an Oracle.
To complete a full game, the player sends two transactions on the blockchain. The first one would register a bet in the contract. The second one should be made in two blocks time (around a minute) and it is used to check for any profit and also transfer it.
The contract can be used by multiple players at once. However the calculation if a player's bet is payable by the contract is done in the web3 frontend. This is vulnerable to a race condition between multiple players.
You can access the game through the web frontend at: https://yordanpavlov.github.io/BlockchainRoulette/
This code is written as an exercise and proof of concept. It is not to be used for betting with real money in no way.