controller for temp?

I am looking into getting a controller, i am curious if there is one that has a fan speed switch in it, i want my inline fan to always be on but normally be pushing slower and when the temp gets too hot i want the inline fan to take off and speed up, =

so my question is, is there a controller that will do this? keep my fan on a low speed until it reaches a certian temp -and then it will turn the fan speed up?

thanks kindly