teratail is a Japanese technical Q&A community for people interested in programming and IT. Members exchange knowledge through two kinds of posts: Q&A for a specific programming problem and discussion for broader topics about programming or IT engineering. Questions can use templates and Markdown; replies and comments help clarify a problem, and the asker can select a best answer to mark it resolved. A clip feature lets users save questions to revisit, while feeds help them browse recent, unanswered, or resolved topics. The service supports PC and mobile, and its official help says registration and all services, including asking and answering, are free.