If you want the full version and license for commercial use,
you can purchase here :

https://staircaselab.com/product/saturday/

File include : 

1. Saturday.otf
2. Saturday.ttf
3. Saturday.woff
4. Saturday Bold.otf
5. Saturday Bold.ttf
6. Saturday Bold.woff
7. Saturday Thin.otf
8. Saturday Thin.ttf
9. Saturday Thin.woff