See below for a list of resources I found useful on the topics of:

Machine Learning and Statistical Learning

Math

Research Software Development

Computer Science
Machine Learning and Statistical Learning
Math
Linear Algebra

Essence of linear algebra: A set of videos providing a friendly and visual introduction to linear algebra.

Linear Algebra: An online course providing and in depth introduction to linear algebra. With exercises.
Calculus

Essence of calculus: A set of videos providing a friendly and visual introduction to calculus topics.

Calculus made easy: A book giving simple explanations of calculus concepts. With exercises.
Probability
Research Software Development
Computer Science