When I visited Paris a few months ago, I found a coffee shop that was specifically targeting people who wanted a place to work, and turned the business model upside down: instead of selling you drinks, and you getting the place for free, they would bill you by the hour, and the drinks were free (and good!). Of course, that means you get to stay as long as you want, no questions asked. The prices were 5€/h or 24€/day, which was totally OK for me as I just needed to work for one day.