Stop guessing which thread your Swift code runs on. MainOrNot shows you in real-time with 🟢 Main / 🔴 Background indicators as you learn. 13 interactive examples covering Swift 6.2 concurrency from basics to actors. Execute code live, see thread execution instantly, understand async/await patterns by watching them run. Includes Swift 6.2's new Approachable Concurrency & Default Actor Isolation flags, learn the future of Swift today. 6 languages.