Introversion Software have updated Prison Architect once again! Update 16 that's currently in Beta adds in cooperative prison building for up to 8 people.
Currently, the Beta is not on Linux. Their previous Betas have been, so we've reached out to see what's up there. The Beta is also only available on Steam right now, while they work on polishing the feature.
Some features are disabled, while they work on getting the core features properly working and synced for multiple people. It's a fantastic addition though, one I hope to try out at somepoint. I can only imagine how chaotic it's going to be, but also quite fun. One person in charge of security, another expanding the prison and so on.