The ARTH Pool is a special token designed to accumulate fees/rewards and distribute them to their token holders.
ARTH Pool tokens work similarly to Uniswap V2 LP tokens. The token contract accumulates fees and by holding pool tokens, users are entitled to a portion of the rewards proportionate to how much percentage of the supply they own.
By using ARTH Pool tokens, the various staking programs can offer rewards in multiple tokens.
The source code can be found on Github: https://github.com/MahaDAO/arthcoin-v2/blob/master/contracts/ERC20/PoolToken.sol
It is deployed on the ethereum mainnet in this address: 0xb4f85c1baffa9ff8c80a07dfad6f0908fe0a749b