z/Scope is a multi-protocol, multi-host terminal emulator that provides access to multiple terminal-based applications in a way that is familiar to every user, using a modern tabbed interface.

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 a terminal emulator in the os & utilities category. There are four alternatives to x3270 for Windows and Web-based. The best x3270 alternative is z/Scope. Other great apps like x3270 are Vista tn3270, Microfocus Extra! and Flynet Viewer Terminal Emulator.
z/Scope is a multi-protocol, multi-host terminal emulator that provides access to multiple terminal-based applications in a way that is familiar to every user, using a modern tabbed interface.

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.

Extra! is a Windows-based terminal emulator that connects users to IBM, UNIX, and Linux hosts. Extra! provides features you need to get the most from your mainframe applications.

Flynet Viewer Terminal Emulator is a zero client, web based solution for accessing green screen applications on Mainframe, Unix, IBM i (AS400), VAX, VMS and may more.
