Program a temperature profile to mash beer or reflow solder. Here's how.
This full featured open source PID controller uses a DIY stripboard shield for Arduino Uno and compatible boards. Firmware based on osPID (http://http://www.ospid.com/blog/) massively revamped and extended, blood was sweated over new auto tune routines. Standalone or remote operation over UART using Java GUI. All documented on Github with BOM, schematics, code, pictures etc. Parts cost about $15, external SSR module and Arduino required.

Hardware (http://http://smokedprojects.blogspot.com/2013/11/stripboard-pid-arduino-shield-hardware.html)
Firmware (http://http://smokedprojects.blogspot.com/2013/11/stripboard-pid-arduino-shield-firmware.html)
GUI (http://http://smokedprojects.blogspot.com/2013/11/stripboard-pid-arduino-shield-software.html)
Thermocouple adapter (http://http://smokedprojects.blogspot.com/2013/11/stripboard-pid-arduino-shield-part-4.html)
SSR module (http://http://smokedprojects.blogspot.com/2013/09/solid-state-relay-module.html)
I spun this project as a kit for Tayda (http://http://taydakits.com/instructions/arduino-pid-controller-shield), with the idea that all the components could be cheaply ordered in one place. It took a while to happen but the project is finally up on their site. Another way to go would be to adapt one of the very cheap LCD shields (http://http://amzn.to/1jFhbQc) that are available.