Mathematics
A collection of resources and tools to be able to aid you into solving mathematical problems.
/r/learnmath
A subreddit forming a welcoming community for people who is interested in taking a test dive into the world of mathematics.
3Blue1Brown
A YouTube channel that focuses on teaching mathematics intuitively by including animations. If you want to get started learning mathematics with this channel, I recommend to look into the playlist (or the Essence of X series).
American Institute of Mathematics Approved Open Textbooks
Quite self explanatory. It's a list of approved open textbooks for a variety of mathematics-related branches such as calculus, number theory, logic, and differential equations. You can also see how these books has been approved through their open evaluation criteria that has been put up on their website.
Anaconda
An open-source platform for mathematics and data science. It's a package distribution with a feature-complete set of tools and libraries for data science (NumPy, pandas, etc.), machine learning (Tensorflow, scikit-learn, etc.), and other mathematical tasks (Jupyter Notebook, Matplotlib, etc.) that can be done with an individual.
Awesome Math (by rossant)
An awesome list of websites, tools, and lecture notes for the branches of mathematics such as topology, calculus, analysis, and more.
Eddie Woo
A YouTube channel led by the titular mathematics teacher who produces online content for mathematics, mainly on pre-calculus topics.
fxSolver
A mathematical solver. Also provides formula for different fields including medical sciences, aerospace engineering, computer sciences, and much more.
Geogebra
A free and open source web suite of mathematical tools. Includes a graphing calculator, a 3D graphing tool, and geometry tools. Also provides mathematical resources for different mathematical branches which you can see in their Resources section.
Mathway
Similar to Geogebra, it provides a free online-based suite of mathematical tools to help in solving problems ranging from algebra, calculus, statistics, linear algebra, and even chemistry.
Octave
A free and open source scientific and computational programming language similar to MATLAB. In fact, it is mostly compatible with MATLAB code (READ: mostly). It is made by the team at GNU Software.
patrickJMT
A YouTube channel that focuses on mathematics so if you want to learn math through YouTube, here is one channel that specializes on it.
Paul's Online Notes
A popular mathematics online notes. Contains cheat sheets and detailed notes on several mathematical subjects like algebra and calculus (and its subtopics).
Professor Leonard
A YouTube channel that focuses on giving topics on calculus.
Personal comment:
Recommended for calculus stuff, also pair this one with Eddie Woo and you got a pair of YouTube channels to teach you the high school math.
Symbolab
A step by step calculator aiding you in solving algebra and calculus problems. One of the main features here is they also provide practice problems and quizzes in the site to help you improve your problem solving skills.
SciPy
A free and open source mathematical, science, and engineering set of Python-based libraries and frameworks.
Sage
A free and open source mathematical software built on top of existing open source projects such as SciPy libraries and many more. Another free and open source alternative to MATLAB.
Understanding Mathematics
A GitHub repo that contains a list of references of various media for you on how to deeply understand the world of mathematics.
Wolfram Alpha
Offers a plethora of mathematical (and non-mathematical) tools.
Personal comment:
What is a mathematical tool list without Wolfram Alpha?
Wolfram MathWorld
An encyclopedia of mathematics-related topics.
Personal comment:
Recommended for pre-calculus concepts. Pair that up with Professor Leonard (another of my personal recommendations) and you have a pair of YouTube channels that teaches high school mathematics for you.