Very professional from start to beginning - Saw the job ad on LinkedIn and applied directly through them. A few days later they contacted me to upload a video answering a few questions. That was followed by an initial interview with HR and the CTO followed by a final interview with the CEO, QA/RA and CTO where I had to prepare a small case study.
At all times the team was very responsive, letting me know if there were any delays in the process and getting back to me if I had any questions. Certainly the most professional selection process I have been through in a start up.