For more information about this project and its native (and new) cryptocurrency ROGUE check out
my post on Medium.
[...] players will be able to swap their earned Tetras for ROGUE at a fixed exchange rate. The platform takes no fees from deposits [...]
If your system allows both withdrawals and deposits of one coin at a fixed rate in tokens, then I think it's not very difficult to add withdrawals and deposits for other coins at a variable rate calculated from available reserves of the coins and of Tetra tokens.
It wouldn't be decentralized, but would work as some cross-chain, Uniswap style exchange.