There's also open courseware, which goes a lot deeper into the material than Wikipedia can or would want to go. And then there's public library.

My grandfather, who was a civil engineer often made the joke of giving the abbreviation for the public library in his hometown (UPL) as the place where he got his education. And it was true, but that was post-Great Depression, circa New Deal era when a civil service exam was enough to start a real career, and a college education was not considered necessary for most occupations.