What is the difference between USDT and FDUSD?

Could you elaborate on the fundamental differences between USDT and FDUSD? As I understand, both are stablecoins pegged to the US dollar, but I'm curious about their unique features, issuance mechanisms, and the entities behind them. For instance, how does their approach to reducing volatility and enhancing financial efficiency differ? Also, are there any notable differences in terms of their adoption, trading volume, or security measures? I'm eager to gain a deeper understanding of these two cryptocurrencies.