Mathematica is a programming environment designed for mathematical computations.
MATLAB integrates numerical analysis, matrix computation, signal processing, and graphics in an easy to use environment.
For resources on learning Python & R, check out the Data Science guide.
LaTeX is a typesetting program useful for mathematical and scientific writings or publications. The Libraries' LaTeX guide provides an overview of how to get started with LaTeX, as well as resources and exercise to help new users of the program.
Comparison of Reference Management Software: Wikipedia article with summary information twenty different citation management tools, including cost, license, import/export formats, citation and reference list formats, word processor integration, and ability to connect to external databases.