Useful math things

Here are some useful math things:

• Desmos is a graphing calculator (and more)

• 3Blue1Brown has excellent content on the fundamentals of calculus and linear algebra

• Paul's Online Math Notes has a bunch of material from college algebra up through differential equations

• OEIS is The On-Line Encyclopedia of Integer Sequences

• Overleaf is a collaborative LaTeX editor

• Detexify lets you draw a symbol and then tells you the LaTeX for it

• Commutative Diagram Drawer makes drawing commutative diagrams in TikZ/LaTeX easy

• The Stacks Project is an open source textbook with lots of algebra

• commalg.org lists upcoming events in commutative algebra

Primarily (but not totally) for math/math ed undergraduates at North American institutions, if you are interested in studying mathematics abroad, then Budapest Semesters in Mathematics (or Mathematics Education) may be of interest.  I did BSM in the Spring of 2019, and it was an incredible experience.