NIST Uncertainty Machine – User’s Manual [pdf] (uncertainty.nist.gov)

Applied statistics is really useful for beginners if it is documented so well like this webpage.

I now have a very good understanding of two widely used uncertainty measurements (GUM and Monte Carlo method) just by reading the first few pages.

This is a fantastic resource, not only because its convenience, openness and reproducibility, but also because of the educative value of the documentation.