Reservation system for shared desks

Good morning fellow sysadmin, hope you're all safe and sane, specially during these challenging times.

​

I got a new task at work, and I'm hoping you guys can help me out with something. I have the whole company working remotely (\~200 users) but my CEO wants a few departments back by July 20th. The plan is to have people coming to the office in alternate days and using shared desks, and it's with this I need your help.

​

I need a system so the users can say when they're coming to the office and which desk they will use, but it has to be free (the CEO doesn't want to spend money on this). Do you know something that might be useful?

​

Thanks in advance