PoolTogether is a No Loss, Prize Savings Account, all deposits are retained by the depositor. Their funds never decrease and always have a chance to win a prize (a portion of the interest received). The deposits from everyone are pooled together to earn interest from yield sources (aave), this yield is then awarded to a subset of the depositors. V4 currently has over 700 winners per day. V4 is also aggregated to be multi-chain (currently Polygon and Ethereum), so regardless of what chain you're on, the deposits from all chains contribute to the prize that can be won.