Zazu is a fully extensible open source launcher. There are binaries that can be downloaded for Windows, Linux and Mac. I'm going to show you how to get started on a mac, but the steps are almost identical on other operating systems.
To download Zazu, go to 'zazuapp.org' and click 'download', then select your operating system. Walk through the steps to install it on your computer, then launch the application for the first time. You'll soon be greeted with a notification telling you that your plugins have finished installing.