Three part interview that went the distance. First was a very brief interview with the company recruiting team. Second was a one hour technical interview with two coding questions, followed by behavioral questions and an opportunity to ask about the company. Third was an onsite interview, four people over the course of four hours. All had a technical side with whiteboarding, ranging from easy to fairly difficult. I was able to answer all of their technical questions correctly within the allotted time, and often had discussions about the company as well. Some were more direct and others very personable, just depended on the interviewer. At the end of the final interview, the interviewer let me know that the next day they would have a meeting to discuss the interviews and I would hear back with "yay or nay" by the end of the day. At this point it was a fairly pleasant experience. Several weeks later, I never heard back from them. I tried reaching out by email and eventually by phone, and was ignored on all fronts. I can understand going with another candidate or being underqualified, but either way there was a given expectation that feedback was going to given quickly. To hear nothing back and to be ignored is just unprofessional and a waste of time. I would be afraid that this type of behavior extends into company.

Connected through a recruiter. 2 round interview process, both onsite. The first lasted about 90 minutes with a single developer (I enjoyed this stage), the second lasted 4 hours with 4 separate developers. All 4 had a technical component, 2 had an additional "fit" component. Fairly standard interview questions (breadth first traversal, stream processing in C#, tic tac toe game, open ended design question). I didn't answer the technical questions perfectly in all cases (was pressed for time at every stage), but felt that I showed competency in most areas. They want to be able to dig deeper and see how well you understand things even at the OS or compiler level.