Atom is a free and open-source text and source code editor. It is useful for many common programming functions and can be customized with third party packages. It was developed by GitHub. It runs on Windows, Mac, and Linux.
GNU Emac is "the extensible, customizable, self-documenting, real-time display editor". It has a very active community and is being actively developed. It has many useful commands but somewhat steep learning curve. AU has several useful guides available online, such as Learning GNU Emacs. It works with Windows, Mac, and Linux.
Postman is "a collaboration platform for API development. Postman's features simplify each step of building an API and streamline collaboration so you can create better APIs—faster." While Postman does have paid plans, the free plan is more than enough to get most beginning coders started. It works on Windows, Mac, and Linux
Sublime Text is a cross-platform editor commonly used for code and prose alike. It supports many languages and can be extended with plug ins. It has a number of useful features for programmers. It works with Windows, Mac, and Linux.
Vim is a highly configurable text editor built for efficiently creating and changing any kind of text. It has a bit of a learning curve, though vimtutor will get you up and running quickly, and is sometimes thought of as a "programmer's editor": it's a tool to use to edit config files, but generally not to write a novel. It works with Windows, Mac, and Linux.
VS Code is a free and open source code editor that was developed by Microsoft but works with Windows, Linux, and Mac. It has many useful features for programmers and is highly customizable.
Apache OpenOffice is a free and open source office suite including free alternatives to Microsoft Word, Excel, and Powerpoint, as well as other programs. It works with Windows, Mac, and Linux.
LibreOffice is a free and open source office suite including free alternatives to Microsoft Word, Excel, and Powerpoint, as well as other programs. It works with Windows, Mac, and Linux.
Open Refine is an open source desktop application for data wrangling. It can transform, parse, and clean data. It is similar to both a spreadsheet and a database, but is used for the specialized purpose of dealing with messy data. It works with Windows, Mac, and Linux.
SAS University Edition is the same powerful software professionals use, but free for students and educators. SAS is used for many purposes, from criminal investigations to business analysis, and students have a wonderful opportunity to gain experience with software used in many industries.
Tableau is an interactive data visualization software. While normally a paid program, Tableau offers students and educators free access with very few restrictions, allowing users to gain experience with this industry standard for seeing and understanding data. It works with Windows and Mac.
Zotero is a free and open source research management application. It has useful collaboration tools and is widely used in academia as a free alternative to EndNote. It works with Windows, Mac, and Linux.
Algodoo is a physics-based 2D sandbox, somewhere between an open ended game and an engineering tool. It is primarily marketed to children and teachers. It includes the ability to simulate fluids, springs, hinges, motors, thrusters, light rays, tracers, optics and lenses, and has a large and active community. It works with Windows and Mac.
SageMath is a free and open source alternative to Mathematica and MATLAB. It can be used for algebra, number theory, calculus and statistics. It works with Windows, Mac, and Linux.
R is a free software environment for statistical computing and graphics. It compiles and runs on a wide variety of UNIX platforms, Windows and MacOS. It is widely used among statisticians and data miners for developing statistical software and data analysis.
Python is a popular coding language. It is highly readable, making it easier for new programmers to learn. Python is developed under an OSI-approved open source license, making it freely usable and distributable, even for commercial use.