Calculus

• Paul's Online Math Notes
• Thomas' Calculus Textbook (though Stewart's is also good - I think it it convoluted in it's explanations at times)
• Calculus in Context (Five College Calculus Project)

Linear Algebra

• Linear Algebra Cheat Sheet (Yiping Lu, 2024)
• Linear Algebra in 4 Pages (MiniReference)

Differential Equations

• Notes on Diffy Qs: Differential Equations for Engineers (Jirka)
• ODE Reference Sheet (UNCW)

Electrical Engineering

• Sanfoundry's 50,000+ Electrical Engineering MCQ's - sorted by year and topic