EtherDelta is a decentralized exchange for trading Ethereum based tokens. It doesn’t have a mobile app, but it does provide support for hardware wallets and has relatively low trading fees.
GDAX: Global Digital Asset Exchange is an extension of Coinbase and provides much of the same functionality. It’s simple to use and has great user interface, making it a good choice for new cryptocurrency users.
Idex: Idex is another decent decentralized exchange available on web, desktop and mobile devices and supports many ERC20 tokens including OMG, ZRX, ICONOMI, VEN, KNC etc.