Abstract Algebra by Judson - https://judsonbooks.org/abstract-algebra-theory-and-applicat...
Linear Algebra by Hefferon - https://hefferon.net/linearalgebra/
Real Analysis by Lebl - https://www.jirka.org/ra/
Differential Equations by Lebl - https://www.jirka.org/diffyqs/
These should be enough to give you a first and second year undergrad level education in mathematics (minus stats&probability).