A fully decentralized, blockchain-based web application in which anyone can participate on or create their own betting pools. There are no limits to what you can bet on; any website can be queried against and have the intended result parsed and uploaded to the blockchain.
I'm making things interesting by starting a bet with a 0.25 ETH initial pool. To put my money where my mouth is, and to honor the many hours and dollars I've lost browsing /r/wallstreetbets, I've created a simple starting bet: SPY_GUESS will query Investing.com to extract the price (without decimals) of the well-known S&P 500 index on Saturday, October 9th 2021, 22:00 UTC. You can place a bet on how much you think it will be worth on that date, the deadline to do so is Sunday, October 3rd, 13:00 UTC.
You can't! All server communication is delegated to the oracle contract, so using WSBDD is as simple as having MetaMask installed and some funds in your account.