I applied for a full-time position during my senior year of college (fall 2016). There were three rounds of interviews - 1 phone, 1 video chat, and 1 at the corporate office.
The phone interview was a recruiting screen; simple behavioral questions, such as questions about my interests, classes, work experience, and life goals. The recruiter was really nice and I felt comfortable during the conversation, which is a big help over the phone.
The second round was a video chat over Cisco WebEx with an engineer-turned-manager. This was a technical interview, where I was asked questions related to the type of software engineering I was applying to do.
Some questions I wasn't able to answer and some I had to guess on, but my interviewer did a great job at making me feel like I wasn't being grilled and gave me all the time I needed to think about answers. There were a few hiccups on their end (i.e. switching rooms and computers due to Internet issues), but, *shrug*.
The third round was at their corporate office in Waltham, MA. I was part of a group of ~15 other college student interviewees. We should up at 9 and were released around 1. We were fed a light breakfast of fruits and assorted pastries (which I missed due to getting lost. FYI, if you drive by the entrance, the road immediately becomes ONE WAY and you have to get back on I-95 via MA Route 2, UGH).
There were 3 or 4 interviews - one or two recruiters and two engineers. All around, the questions were significantly more specific and difficult than those over the phone. The recruiter I spoke with wasn't super lax, but the engineers were again great at making me comfortable and helping me with stuff I didn't know once I was at a whiteboard.
Their office (the very small bit that I saw) was very nice. Clean and modern, with lots of glass and people wearing a mix of casual (jeans/sweatshirt) and business-casual attire. They reimbursed for gas too!
Turned out the team that wanted me wasn't based in Waltham, so at my request I had a 4th round of interviews at their location. I met said team and a few managers in formal interviews and was subsequently taken out to lunch by the entire team. A much smaller office with far fewer employees, it was still pretty nice. They had a small kitchen, but big windows, and everyone was really nice.
Overall, my experience interviewing at Carbon Black was probably the best of all the ~5 places that I ultimately got on-site interviews, and definitely the best in terms of ~12 companies I had phone interviews with. I had a lot of other great experiences, but something about Carbon Black gave me a positive gut feeling and I ended up accepting their offer.
Hope this helps you!