smcFanControl lets the user set a minimum speed for built-in fans. It allows you to increase your minimum fan speed to make your Intel Mac run cooler. In order to not damage your machine, smcFanControl does not let you set a minimum speed to a value below Apple's defaults.
Make sure you have both [Homebrew](http://brew.sh/) and [Cask](http://caskroom.io/) installed. You'll find intructions to install both tools on their respective websites.