This is a clean Ubuntu 16.04 base layer with Swift installed on top. It's for use as a Swift base layer.
You could for example expose a folder in your local file system to this container, use the local folder to write your Swift code, and use the container to build, run and debug your Swift code.
I created this container because Swift.org's download bundles by default use /usr, and I did not want to clutter up my local filesystem. By installing Swift in a container I can still develop in Swift on Linux, but I don't need to install Swift locally.