Cryptox simply allows you to exchange one cryptocurrency for another using the ChangeNOW API.
Until I can get acquire a ChangeNOW private key, you'll need your own ChangeNOW API key to use this.
Fair warning, I do believe they collect their own fees in addition to mining fees, etc.
Additionally, I believe I also make a small amount (0.3% to 0.4% of the exchanged amount) per exchange. Though, that only happens when my API key is used to create the transaction.