First you'll have a quick call with one of their HR reps who are by all accounts great to deal with. Second you'll meet some of the members from the department you'll be interviewing for, this is where things kind of fell off for me. This step seems to be more of a screening process than anything else likely because the Third Step involves you meeting with someone who actually has the decision making power, so keep in mind the pressure is on this first group to be pushing serious contendors to their senior managers. Problem is, seems like most of the people interviewing you at this step have limited knowledge of how things work outside of their current domain so when you're answering questions make sure you don't talk too much about things that a SCRUM Master wouldn't directly be dealing with because chances are the people interviewing are in their first PM type role so it will go right over their head and they likely won't be able to appreciate the value of what your saying.
Advice to those interviewing:
Step One: Be yourself and talk to the HR rep like you would talk to anyone, be open, transparent, and down to earth.
Step Two: Don't walk in and get caught up in the perceived culture, although it is relaxed and definitely something to admire, their focus for the interview isn't on personality at all, regardless of what you have on your resume, they want to hear that you've done something exactly like what they are doing now.
Step Three: Although I don't have experience with this step, you'll likely be meeting a more senior member that has to in turn worry about the team dynamic of his/her group, so this might be the time to kick that charm back into play.
Advice to FreshBooks:
No Disrespect meant by this, but if you're going to have people interviewing others for a position at least make sure they're experienced enough in their field to understand not every workplace is the same and that there is value in experience from roles outside of the ones in direct unison with their own. Also, if your concern is technical knowledge, ask technical questions.