QoWS is a plugin for the Eclipse framework, you can download it from the official web site.
Download the QoWS plugin bundle from here and unzip it into the eclipse plugin folder.
Before running the workbench, you need to install also the following plugin and external dependencies:
To use QoWS you first need to configure it: you need to specify where the workbench can find PRISM and JMT.
Launch Eclipse, navigate to the menu
and set the path where you installed PRISM and JMT.
If you want to play with the workbench out of the box, you can download a zipped project from here and import into into your workspace.