MartyPC.net is a web-based emulator that lets you run classic PC/XT software in your browser. It's built by a developer who goes by GloriousCow and is hosted on Cloudflare with a valid SSL certificate and a clean reputation history. For a hobby project, the site is unusually well put together – it has an about page, a privacy policy, and even terms of service, which most one-person emulator projects skip entirely.
Because this site doesn't ask for payments, logins, or personal information, the usual e-commerce concerns don't apply. The only question is whether the emulator itself works as advertised, and that's easy to test since it runs right in the browser. If you're looking for a safe way to play old IBM PC games or experiment with retro computing, martypc.net looks like a legitimate and well-maintained resource. As with any software running in your browser, it's still a good habit to check what permissions the site requests – here, none are needed beyond running JavaScript.