Monero, It's great for darknet stuff, but in Russian darknet marketplaces everyone uses bitcoin. Tron, great platform for moving USDT, but now Polygon is cheaper. Every EVM blockchain is pretty much a platform for moving USDT, It's their only real use case. I think of them as a payment providers such as PayPal, but more open and decentralized (of course not as decentralized as bitcoin, but better than PayPal).