Most market hours sites are cluttered with ads and news, and don't directly answer the simple question: "What markets are open right now?" So I built a site that does exactly that:

UTC and your local time Which major markets are open/closed Countdown to next open or close

Markets included: NYSE, London, Tokyo, Hong Kong, Shanghai, Frankfurt, Sydney. Also handles lunch breaks and holidays. That's it. No ads, no news, no clutter.