Talking of synthetic assets, Mixtrust is first in mind. First of all, Mixtrust is a decentralized platform that allows users to trade in a decentralized and trustless manner by avoiding the need to go through a third party organization.
Its protocols are ethereum based, it provides decentralized cross chain trading for synthetic assets and also cross chain mortgage lending. It is a distributed, open source and integrated DeFi ecosystem. It supports all kind of synthetic assets and swaps, this could be done by transferring them through Mixtrust decentralization in exchange for actual currencies. There are also rewards for Mixtrust holders which makes it even interesting