You can trade on the XRPL DEX[1] (The oldest DEX) essentially for free* since it went online. The DEX works like a central limit order book which limits the way you can trade. There are also liquidity problems for many currency pairs as well as counter-party risk if you trade/hold IOUs with a counterpart like for example Gatehub USD stable coins (Counter-party here would be Gatehub so if they go bust Gatehub USD is likely going to be stable at zero).

For a more advanced use of the XRPL DEX there is Sologenic[2] which is build on top of the XRPL DEX.

[1] https://xrpl.org/decentralized-exchange.html [2] https://sologenic.org/trade

*Free as in no one earns money from your usage. There is a tiny fee burnt to prevent spam for each offer/transaction. A typical fee is under $0.0001.