I came across this player while going through useronboard.com. In the posts area, there is a discussion about the jobs-to-be-done concept with Ryan Singer from 37signals. When I landed on the page, I saw this super sleek and minimal audio player and I just had to find out where it was from and how it was built.
Looking at the source, it seems to be a jQuery library called, jPlayer. Looking at the library’s site, it looks like useronboard.com did some tweaks to make it look like how it does. Definitely will try this library out in a future project.