In Seoul, South Korea, there are several popular cryptocurrency apps that are widely used by the local population. These apps provide users with the ability to buy, sell, and trade various cryptocurrencies, as well as access market data and news. Below is a ranking of the top cryptocurrency apps based on the number of downloads in Seoul:

1. Upbit: Upbit is one of the largest cryptocurrency exchanges in South Korea and is extremely popular among Seoul residents. The app allows users to buy and sell a wide range of cryptocurrencies, as well as access real-time market data and news. Upbit is known for its user-friendly interface and strong security measures, making it a top choice for many cryptocurrency traders in Seoul.

2. Bithumb: Bithumb is another popular cryptocurrency exchange in South Korea that is widely used in Seoul. The app allows users to trade a variety of cryptocurrencies, as well as access market data and news. Bithumb is known for its high trading volume and liquidity, making it a top choice for traders looking to buy and sell cryptocurrencies quickly and easily.

3. Coinone: Coinone is a cryptocurrency exchange that is also popular among Seoul residents. The app allows users to trade a variety of cryptocurrencies, as well as access market data and news. Coinone is known for its strong security measures and responsive customer support, making it a trusted choice for many cryptocurrency traders in Seoul.

4. Korbit: Korbit is another popular cryptocurrency exchange in South Korea that is widely used in Seoul. The app allows users to trade a variety of cryptocurrencies, as well as access market data and news. Korbit is known for its user-friendly interface and fast transaction speeds, making it a top choice for traders looking to buy and sell cryptocurrencies with ease.

5. CoinDesk: CoinDesk is a popular cryptocurrency news app that is widely used in Seoul. The app provides users with the latest news and updates on the cryptocurrency market, as well as analysis and insights from industry experts. CoinDesk is known for its comprehensive coverage of the cryptocurrency market, making it a top choice for traders and investors looking to stay informed.

Overall, these are some of the most popular cryptocurrency apps in Seoul, South Korea, based on the number of downloads and user reviews. Each app offers a unique set of features and benefits, so it's important for users to research and compare their options before choosing the best app for their cryptocurrency trading needs.