Sage is a free open-source mathematics software system.  It’s a GPL alternative to commercial software such as Magma, Maple, Mathematica and MATLAB.  Sage is a research-grade tool, cited in nearly 100 academic research articles (with dozens more in press).

I’ve written a book to help engineers, scientists, and students get started with Sage.  It’s available in print and e-book formats.  Please check it out!