Crosstalk Mk.4 was a commercially available PC telecommunications and terminal emulation software package originally produced by Atlanta-based Crosstalk Communications, from the late 1980s through 1990, and by Digital Communications Associates until the mid-1990s. Crosstalk Mk.4 was one of a suite of products produced by the company; others included the famed Crosstalk XVI, Crosstalk Communicator, Crosstalk for Windows, and Remote 2.
Featuring multisession communications capabilities, Crosstalk Mk.4 allowed multiple serial ports to be used and controlled simultaneously. A powerful programming language called CASL (Crosstalk Application Scripting Language) provided full program and communications activity control, and enabled users to create a wide variety of custom applications.
The program was in widespread use globally and served the communications and equipment control needs of major television networks, pharmaceutical companies, oil producers, and North American real estate listing providers, among many others.