The GitHub Code Search feature is really useful. If I run into a weird problem that's somewhat outside "mainstream" programming (e.g. 2D Line Arrangements with CGAL), I'll often use Code Search to try to find repos that are using the API I'm using to see how they used it.
Hmmmmm that’s an interesting question! I think the GitHub search has a better semantic understanding of what I’m looking for, but I’m going to have to try it out!