Rieul Korean is an Android app developed by Rieul that offers a wide range of features to help learners of the Korean language. The app includes a dictionary browser that allows users to swipe between definitions of a word in different language dictionaries, such as Korean-English, Korean-Korean, Korean-German, and Korean-Japanese. In addition to this, the app also offers lookup, self-testing, and reference information for verb/adjective conjugation, pronunciation, and numbers.

One of the standout features of Rieul Korean is the tests it offers for times, dates, counters, money, and age. These tests help learners improve their comprehension and usage of these common aspects of the Korean language. Another impressive feature is the 10,000-word vocabulary browser that enables users to find words that share the same hanja. Additionally, the app provides definitions and tests for 70 four-character idioms (고사성어), which are commonly used in Korean literature and conversation.

Overall, Rieul Korean is a comprehensive app that offers a variety of features to help learners of the Korean language improve their skills. From the dictionary browser to the tests and vocabulary browser, this app provides a well-rounded approach to language learning.