First of all, I had a very pleasant experience and would recommend Secret Sauce Partners to anyone looking for a great team with interesting products and technologies and a culture of transparency.
The process took 1.5 months, and consisted of a fairly easy online HackerRank test (3 tasks in 60 minutes, 2 coding/algorithmic exercises and an essay), a review/discussion through mailing on implementation details. At this point, I was signed an NDA. An in-person technical interview followed with two developers, a more personal interview with the team manager and two sessions with the CEO through Skype. There was an assessment day as well.
The technical interview was more of the "how you see.../what do you think about..." type and covered certain aspects of JVM, multithreading, testing, OOP and HTTP.
The team manager interview was more about culture fit and team-fit aspects with HR-like questions on strengths and improvable skills, etc.
The interview with the CEO was split into two parts due to limited availability, first one being a more personal one on my personality, goals, views, and the second one was on startups generally.
There was also an assessment day where I had to implement the back end of a web service in a chosen language/framework. This day was finished with a 1-on-1 assessment and was followed by a detailed code review from the other technical interviewer.
The whole process was well-coordinated, all participants were very responsive throughout the selection.