The outbreak of COVID-19 has pushed many teachers and students to change their traditional ways of teaching and learning, which also required them to become more familiar with using various online resources. UNESCO emphasized that more quality open educational resource (OER) materials should be made available to teachers and students. Compared to many commercial sites, OERs have been constantly criticized for their poor quality (International Commission on the Futures of Education,
2020
). However, so far, insufficient attention has been paid to the improvements and promotion of OERs. To fill this important gap, this paper first introduces how we use various computer-assisted language learning (CALL) and natural language processing (NLP) technologies and the free resources around the world to develop a comprehensive open-source English learning site called Cool English. The content and major functions of this site are first introduced. An investigation on how the site helped teachers and students during the COVID-19 time (from February to July 2020) was carried out by analyzing the various resources used by teachers and students. In addition, we also discuss several problems and challenges of using this website and other online resources. Through the descriptions and analyses of this website, researchers might be able to gain some experiences in developing and promoting OER sites for English language learners and teachers.