The empty CIShell framework can be downloaded from our GitHub page. However, because the CIShell framework starts out with no plugins inside it, it can be an intimidating place to start exploring.
We recommend downloading Network Workbench or Sci2, two existing CIShell-powered tools that can easily be extended, and trying to develop a new plugin in one of those environments first. The CIShell Algorithm Developer's Guide will help you through your first steps.
Once you create a new algorithm or two in those environments it should become more clear how to build an entirely new CIShell-based tool from scratch. If you are interested in developing a new tool based on the CIShell framework, we would love to hear from you and offer our assistance.