Check out my books on CALCULUS+MECHANICS, and LINEAR ALGEBRA: https://minireference.com/ They are not free, but not expensive. It's like 2 years worth of undergraduate maths packed into two small books.

Previews are free though, and might be useful if all you need is an overview: https://minireference.com/static/excerpts/noBSguide_v5_previ... https://minireference.com/static/excerpts/noBSguide2LA_previ...

This is also good: http://ml-cheatsheet.readthedocs.io/en/latest/