If you run a business and are using Shapecss in a revenue-generating product, it makes business sense to sponsor ShapeCss development: it ensures the project that your product relies on stays healthy and actively maintained. It can also help your exposure in the ShapeCss community and makes it easier to attract ShapeCss developers.
If you are an individual user and have enjoyed the productivity of using ShapeCss, consider donating as a sign of appreciation - like buying me coffee once in a while :)
As of now I am exploring the possibility of working on ShapeCss.js fulltime - if you are a business that is building core products using ShapeCss.js, I am also open to conversations regarding custom sponsorship / consulting arrangements. Get in touch on Twitter.