x3270 is described as 'IBM 3270 terminal emulator for the X Window System and Windows. It runs on most Unix-like operating systems -- e.g., Linux, Mac OS X, Solarnd Cygwin. It also runs natively on Windows' and is an app in the OS & Utilities category. There are six alternatives to x3270 for Windows and Online / Web-based. The best alternative is z/Scope. Other great apps like x3270 are Vista tn3270 (Paid), Attachmate Reflection (Paid), Microfocus Extra! (Paid) and Flynet Viewer Terminal Emulator (Paid).
Vista tn3270 is a Windows program designed to emulate IBM 3270 terminals connected to a host via IP link. If you are looking for an emulator created with mainframe programmers in mind, then give this one a try.