Announced by one of the members in our forums is a new open-source program called TurionPowerControl. The TurionPowerControl program supports both under-volting and over-clocking of AMD CPUs. Currently supported by this program are AMD K8L (11h) and K10 (10h) CPUs, which includes the Turion RM, Turion ZM, Phenom, Phenom II, and Athlon II brands. Originally the developer just designed this tool to support the mobile Turion processors for under-volting, but support was added for these desktop CPUs too. The K8L support is considered the best at this point while the K10 support is still a work in progress.
Besides being able to change the operating frequency and voltage, this open-source program for AMD processors is also capable of setting the Northbridge operating voltage, monitoring CPU performance counters, listing processor features, and more. TurionPowerControl is also compatible with Microsoft Windows operating systems.
We haven't yet tried out this program yet, but those interested can find the download link and more information in this Phoronix forum thread. It sure would be nice to see better Intel/AMD CPU manipulation and overclocking support for Linux along with similar utilities for motherboards.