The term embedded is typically used when talking about software hidden within a hardware appliance in a manner not normally seen. See "What 'embedding' means".

Software within your television, VCR, CD, MP3, DVD players, microwave, or router are all examples of some degree of embedding.

Tcl is frequently used for embedded systems.

Where is Tcl Embedded?

Cisco IOS
User Interface is a Tcl interpreter
F5 Networks
iRules scripts are Tcl scripts
Tcl is embedded in TiVo's digital video recorder system TiVO. See also TivoWeb
VMD - Visual Molecular Dynamics

Where is Jim Embedded?

jimvim ,by Mark Janssen

Tcl in other Embedded Applications

an Active Script interface for Tcl
appbox , by Roy Keene
the base of a modular application delivery system, built on a Linux kernel where init is a Tcl interpreter.
an embedded Linux distribution that uses Tcl for everything from init up

RFox: Software embedded in devices that is not expected to be user configured is sometimes called (by me): "toasterware"

The Embedded Configurable Operating System (eCos) is a free and open source real-time operating system intended for embedded systems. It is designed to be customizable to precise application requirements of run-time performance and hardware needs. The customization is done via a custom configuration language which is delivered as an extended Tcl interpreter; all configuration files are Tcl scripts.

The Jim interpreter runs under eCos.

QP (Quantum Platform) is a family of lightweight, open source software frameworks for building responsive and modular real-time embedded applications as systems of cooperating, event-driven active objects (actors).

Developed by the company Quantum Leaps, the framework provides a modern, reusable architecture based on active objects (actors), hierarchical state machines, software tracing, UML graphical modeling, and automatic code generation.

Uses Tcl for GUI, network communication and script control. Dual licensed: commercial and GPL.