Reading the documentation, it seems to implement most (all?) of the Web Canvas API[1], and in certain areas extend the API in some exciting (well, exciting to me[2]) ways. The key point is that this can be used in the backend, far beyond the browser environment?
[2] The things that jump out to me as "exciting extensions" beyond the Api include: multiline text and text decoration (underlines!)[3]; perspective effects[4]; and Path2D boolean and filter operations[5].