Some hardware has a kind of broken fan-control and lets the fan run
faster than really needed. Thinkfan will prevent this by controlling
the fan on its own (the fan speed for each temperature interval can be
adjusted in the configuration file).
.
Originally designed specifically for IBM/Lenovo Thinkpads,
it supports any kind of system via the sysfs hwmon interface.
It is designed to eat as little CPU power as possible.