On Triplebyte's website there's a timed quiz that you take before moving onto later steps. You're given 40 minutes to complete it, although in my case only 25 minutes were required. All questions were multiple choice and involved either identifying the fix for a bug, choosing the correct completion for a section of code, or answering questions about the appropriate solution for a specific problem.
After I passed the quiz, a section of the website opened up allowing me to schedule the next step in the interview process. This is usually a 40 minute phone screen followed later by a two hour "on-site" interview. In my particular case, based on my quiz performance, I was able to schedule the two-hour interview directly.
I had a choice of either coming on-site to their office in San Francisco or conducting it over Google Hangouts. I chose Hangouts. At the beginning of the interview I was given the choice of a few different problem areas, all of which were generally described on their website beforehand after I finished the quiz. I chose one of the areas and was given an hour to code up a solution to the problem.
After the hour was up, we took a short break and then there was a short coding question similar to what you might find in the easy section of leetcode.com. Then we moved onto general design questions where I provided solutions and we dove deeper into the problem based on the solutions I provided. Then the interview ended and my interviewer told me that they'd contact me the next day to tell me whether they'd work with me, or if they felt I needed to improve where they'd give me specific tips on how I could improve. Luckily, they decided to work with me ;)