The term NX stands at least for two products:

• NX remote access framework (see http://www.nomachine.com/developers.php).
  Mark comments, "... positively impressed by NX's performance, working on my old pentium laptop from work is almost as fast as working locally. Added plus is the possibility to connect through a proxy."
  [Explain pertinence to Tcl.]
• NX is used as abbreviation for the Tcl extension Next Scripting Language, a scripted OO langauge based on the Next Scripting Framework NSF
• Siemens NX, an advanced high-end CAD/CAM/CAE software package. It uses Tcl for a variety of scripting tasks.