Free resources for learning differential equations

Keep in mind that it's not enough to watch videos, you must also engage with problems. You can find problem sets in the courses or textbooks linked below.

Playlists and digital courses:

• Course by Paul's Online Notes
• Course by Khan Academy
• Playlist by Professor Leonard

Textbooks:

• Elementary Differential Equations with Boundary Value Problems
  by William F. Trench
  PDF
• A Friendly Introduction to Differential Equations
  by Mohammed Kaabar
  PDF
• Differential Equations
  by Charles Bergeron and Jiri Lebl
  PDF
• Notes on Diffy Qs: Differential Equations for Engineers
  by Jiri Lebl
  PDF
• Introductory Notes in Ordinary Differential Equations for Physical Sciences and Engineering
  by Marcel B. Finan
  PDF
• A Second Course in Elementary Differential Equations
  by Marcel B. Finan
  PDF
• A Second Course in Elementary Differential Equations: Problems and Solutions
  by Marcel B. Finan
  PDF
• A First Course in Quasi-Linear Partial Differential Equations for Physical Sciences and Engineering
  by Marcel B. Finan
  PDF
• A First Course in Quasi-Linear Partial Differential Equations for Physical Sciences and Engineering Solution Manual
  by Marcel B. Finan
  PDF
• Lectures on Differential Equations
  by Craig A. Tracy
  PDF
• Difference Equations to Differential Equations
  by Dan Sloughter
  PDF
• Calculus and Linear Algebra. Vol. 2: Vector Spaces, Many-Variable Calculus, and Differential Equations
  by Wilfred Kaplan and Donald J. Lewis
  PDF
• Random Differential Equations in Scientific Computing
  by Tobias Neckel and Florian Rupp
  PDF
• Multidimensional Inverse and Ill-Posed Problems for Differential Equations
  by Yu. E. Anikonov
  PDF