WebKit is the only open source project I've ever needed to dig into which immediately signaled onerous complexity, and did not disappoint on that instinct until I gave up. You, too, can have this experience, if you really want. Take a weekend, if you've been programming for a couple decades -- more, way more, if you haven't -- and just try to build WebKit. Go to the repository, follow the instructions, and just try to build the project.

That anybody would -- or could -- dig in, tear it apart, and try to make something better... That is impressive and I salute you.

Edited to add: I am however only interested in using open source applications on Linux, so I'm out on this one, unfortunately. That's not strictly true -- for example, I use ST3 as my daily driver -- but I've got to see a substantial value proposition to weight my decision towards becoming a user. Still, impressive nonetheless, and best of luck to you in this endeavor!