(Note: This blog post was originally published under my old domain(codesmiles.com), here. Web Archive link.
AutoHotkey is a great FREE and open-source tool you can use to create hotkeys and assign them to commands that you can execute on your system. You are asked to create a script file with commands and then open it in the AutoHotkey program to use it. Commands are executed based on the hotkeys assigned to them in the script.
In the script, you can specify simple commands like the one shown below.
The above command launches Notepad.
# stands for Windows key, ^ for Control key, ! for Alt and + for shift
You can find more commands and general usage info about AutoHotkey in the tutorial page here.