The goal of the Tcl-CM3 project is to provide open source tools that that are suitable for developing applications on Cortex-M3 based processors. Currently, the project is providing three packages of tooling.

Debugging Tools
Single Threaded Software Architecture
Translator to Generate Code for the Architecture

The Cortex-M3 is a relatively new microcontroller core from ARM®. The Tcl-CM3 project is an open source project to develop a set of tools specifically aimed at the Cortex-M3. The first set of chips containing a Cortex-M3 core were delivered by Luminary Micro® as their Stellaris® series of chips.

The Tcl-CM3 project is hosted at Sourceforge and the software can be downloaded from there.

References

The Tcl-CM3 has a very narrow scope and is specifically oriented to the Cortex-M3. If you need access to ARM on-chip debugging capabilities for other architectures see the Open OCD Project.