I applied to HubSpot's summer intern program through their website. After submitting my cover letter and resume, I was contacted within 2 hours to set up the first interview.
1) Video interview where a question would pop up on the screen, you have 30 seconds to think, then 1 minute to answer before the video stops recording. There were probably 5 questions total, two of which were "What is your marketing superpower?" and "Explain inbound"
2) Phone screen with a recruiter, definitely felt more like a conversation. Questions were largely behavioral, also asked what I was looking for in an internship experience/what I hoped to gain.
3) 4 30-minute interviews at the Cambridge office (after a brief office tour with the recruiter) with various hiring managers and directors. I was asked questions for about 15-20 minutes each, then the rest was for me to ask them questions, so do your research and be prepared to carry the conversation and ask follow-up questions. All of the questions I was asked were either about my resume (tell me more about X), or how I think/approach a problem. Also keep in mind that they hold all of the intern interviews on one day, so you'll be around other college students, but thankfully there were no group interviews.
Overall, it was a very lengthy process, especially for a summer internship position, but I am sure that they are also looking at us as potential future full-time employees. By the time you get invited into the office, they know you are capable of doing the job. At that point, it seems to be more about fit between what your skills/interests are and the projects they have in mind for the summer. So, do your research on HubSpot re: their culture, current projects and company goals, etc. I easily spent over 20 hours preparing. These positions seem quite competitive to get, but the process was very pleasant. The recruiter called me to let me know their decision and encouraged me to apply for a full-time position when I graduate, which helped with the disappointment having gotten that far.