We had something like that at my work. From June-Aug we had "Summer Hours" where we would not have any meetings after 2pm and could stop working if then if there was nothing vital. Not exactly half day but still nice, though not sure why it's just for summer time...

The thinking is probably that more people are likely to be heading somewhere for the weekend in the summer or at least doing some Friday evening activity.

In general though I observe that I'm seeing a lot fewer scheduled Friday meetings than on other days and, while things sometimes need to get handled on Friday afternoon, people are often pretty apologetic is they schedule a Friday PM meeting.

Better to do 9 days in 10 or really make it to 4 (longer) days, IMO. Because then you're saving some commuter trips for people who have to be on site.

I think 4x9 as a nominal workweek makes a whole lot of sense. (9 days x 8 hours) / (2 weeks) is almost as good.

My company started 1/2 day Fridays a few months ago in what was billed as a temporary experiment. Today it was announced that we'd be keeping them permanently. From my point of view it has been a big improvement for everyone there. Having some time to play with my daughter during the day time is great, especially during winter while the days are short and the sun is already down by the time I am done working.