When I first conceptualized the idea of having my own website back in 2006 when I first started teaching at a collegiate level, Paul’s Online notes was the inspiration. At the time, it was no where near as polished as it is today. The background was a mustard yellow, there was no interactive buttons for showing / hiding solutions. It was simply straight content with links that moved you through the topics and switched from course to course.
The thing I loved about it is that it was solution / example driven. He would show the basic derivation so you know where the formulas utilized came from, thus your not just blindly applying equations. However, after the derivation, it was example after example after example. Which as an engineer, this is what I believe we live for. Show us the theory, the derivation, the possibly pitfalls, the approximations that may be included with the “final form”. But then show me how to apply it in all the weird ways so I can copy / synthesize that myself and extrapolate the solution process into a more general way.
Now personally, my goal with my site is to eventually have all engineering courses, e.g. Statics, Dynamics, Thermodynamics, Aerodynamics, etc… However, we are in a math class for Engineering Majors and for that, Paul’s site is fantastic. Even at the time that I put my site up being proud that I have suppressed solutions, i.e. more interactivity, within a few weeks / month he upgraded it to what it is now, which I believe is a fantastic resource for students.