Ask HN: What do you use to familiarize yourself with other people's code?

I normally end up using Smultron to read code because it allows me to have a bunch of files open and can easily be navigated with the mouse. It also has highlighting for most languages, but there's a lot to be desired with this; namely, there's no way to jump around to where functions are defined, nor are there many other conveniences. I'd prefer to not have to resort to learning an IDE, and would prefer a solution that works with multiple languages, but for right now, support for C and/or PHP is all I really need. I'm primarily working on a Mac, and would be super ok with a web based solution. Any ideas are greatly appreciated!