Poloniex is a cryptocurrency exchange that provides a platform for buying and selling various cryptocurrencies. They offer over 400 cryptocurrencies for trading, including new listings. Poloniex also provides futures trading with up to 100x leverage, cross margin trading with 3x leverage, and an earn feature for crypto rewards. They prioritize security with a multi-layered risk management system and offer a mobile app and API for convenient trading. They are known for their trusted and stable platform and provide 24/7 support.