You could try Brain.fm. It’s supposed to help focus, but I’m not sure it helps any more than other ambient music.

I second SomaFM. But I’m more of a Groove Salad listener.

There are a ton of good challenges on leetcode. I’d use a [virtual] whiteboard and have the candidate ask questions. When I’m hiring, I want engineers who can ask clarifying questions. I don’t want someone who takes an incomplete set of requirements and goes off and builds what they think is the solution. I prefer they use pseudo code and not worry about syntax. Their IDE of choice would correct the minutia. I once had a candidate ask me if I thought design pattern X would be a good fit for the solution. Excellent question. That shows me they are thinking critically about the problem and open to peer input.

If you go with the programming puzzle type challenge, have a few in your repertoire. I’ve seen candidates totally blank on puzzle A, but rock puzzle B and vice-versa.

Things that have turned me off in interviews:

• ask me to write code in a specific language, then nit pick spacing, exact syntax, etc. They can fuck right off. I’m not working for your micromanaging ass.
• invite me to a 1 hour interview with HR, 1 hour interview with my potential boss, followed by a two hour technical interview. After about 2 hours, I’m done, and need a break. A 30h take home would be a hard pass.

Good luck on the hiring process!