Superposition is a free download and will remain free, made possible thanks to the Adobe Fund for Design and Polypane.
The Superposition Design system generator will be a paid extension, planned to be released Q1 2020.
Superposition works on Windows, Mac and Linux. On Windows, our signing certificate is not yet trusted (because it's new) so it will give a warning when you try to install. If this happen, click on "More info" and verify that the publisher says "Firstversionist B.V.". If it does, you can safely install it.
On Windows and Mac the application will automatically update to new versions. We have a lot of updates planned, such as including gradients and text shadows. So in time the app will become more and more useful. Linux users will get an update notification and can download and install updates.
Superposition loads in your web page and intelligently extracts the design tokens used on the page. It categorizes them and transforms them into consistent formatting for you to export.
Many websites includes styling that doesn't get used on a web page but that might also contain design tokens. We filter these out so you don't end up with the wrong design tokens.
Because Superposition is free and most of our time is spent on Polypane, we have limited capacity to provide support for Superposition so it might take a while before we get to your question. If you have questions or remarks, you can reach us on Twitter: @SuperpositionDS, our DM's are open, or email us.