For any sysfs-enabled ROM e.g most custom ROMS:

* Easy GUI to set frequencies, <a href="http://forum.xda-developers.com/showpost.php?p=27955261&postcount=1">governors</a> and <a href="http://forum.xda-developers.com/showpost.php?p=23885668&postcount=1">I/O schedulers</a> (Links on XDA)

* "Safety Valve" to avoid boot-loops in case of unsafe settings (enabled by default)

* Stats screen to see the effective usage of frequencies

Requires root: Yes. The files in question are in /sys and /system.

Creator