I did onsite interviews at Apple and Palantir through Triplebyte. They have been really fantastic at helping me with the whole process, and I recommend them highly. Just be sure to study beforehand, especially on topics such as low-level programming concepts, concurrency, databases, scaling, web development, data structures, algorithms, and so on. They have a comprehensive evaluation in their own interview process (which you get to after doing an online test) that goes over several areas: a greenfield programming project that is pretty straightforward that you have a half hour to do via screen share, another project where you need to debug an application given some failing tests (again in a half hour), and two sessions of questions on the topics mentioned. The idea is that they’re looking for areas where you are strong: there is no expectation that you’ll be able to ace every section. In my opinion, it’s a pretty well-considered setup. I went directly from the initial quiz to the two-hour interview, but there can be more steps based on your performance on the quiz. On the quiz, it helps if you can squint and reckon what code is trying to do in a language you haven't used much before, since many of the most popular languages are used (Java, C++, Python, Ruby, etc.). There are also system design questions, where it helps to try to use "common sense" (for programmers) at times. The onsite interviews with Apple and Palantir required only a half-hour phone call discussing my interest in the company prior to being fast-tracked for the onsite. Pretty awesome!