I'm not maintaining this anymore but dgraziotin's fork is quite active. Go there :)

This is a daemon that uses input from coretemp module and sets the fan speed using the applesmc module. It includes a PKGBUILD for easy installation in Arch Linux.

Based on:

• http://allanmcrae.com/2010/05/simple-macbook-pro-fan-daemon/
• http://allanmcrae.com/2011/08/mbp-fan-daemon-update/
• https://launchpad.net/macfanctld
• http://paste2.org/p/862259
• http://www.lobotomo.com/products/FanControl/