GitHub Compare View goes cross repository
github.com
github.com
It's just so damn pleasant to use. It helps that a lot of really "neat" projects are hosted on it as well.
I'd like to add that I really like their funding model. I feel like it is very sustainable and I don't have to worry about them loading the site up with ads or something to make it work. Our interests are aligned because it's paid for by the developers themselves. They make awesome tools for me, and I pay for them.
I feel like this is an important and underappreciated aspect of their service.