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.
[1] The program was in widespread use globally and served the communications and equipment control needs of major conglomerates.
The company having been acquired and reacquired, as of 2018 the CASL scripting language is supported by Micro Focus's InfoConnect Desktop offering.
[2] ".. first announced in 1985 and then reannounced in mid-1987 ... well worth the wait" was the opening to a January 1988 PC Magazine review.