Ask HN: 4-day week startup list?

37 signals has a similar experiment,

"Back in 2008 we shared some of our workplace experiments including the four day work week (still in effect May – Oct), ...." mentioned at: http://37signals.com/svn/posts/3186-workplace-experiments-a-...

and the 2008 article: http://37signals.com/svn/posts/893-workplace-experiments

Maybe we can put a list together ourselves - the only startup I know doing this is Treehouse.