I was called by the HR for preliminary questions.
Then few days after I was invited to present myself, my background and my motivation for the position . Few days after the presentation, they informed me that I had been promoted to the next step which consisted to make a technical report by answering to five technical questions. I submitted the report and I was invited ten days after for the final interview where I met the two HRs and people working in the company.
We were reciprocally not convinced of each others. I didn't receive an offer.
The impression I got is that they hire highly qualified personnel (polite people, with PhDs) to work very hard but for unspecific "brilliant" ideas of the managers. I found the whole story of the technical report during the recruiting process very unprofessional, especially for the type of questions ( about the specific technical problems they are trying to solve, but without giving any information about the product. Chose, guys: either one or the other). I have never encountered the unpleasant attitude of the male recruiter anywhere else. Indeed, in multinationals much more famous and structured than this small startup, I have met much more professional and humble HR people.