Unity Personal for one day fun in a big organization?

Hi
I know about Unity Personal and Pro. I work in a big organization (more than $100.000 profit a year) and would like to make something with Unity for a day or two. Whatever we’ll make is only for fun and will not be published or made money with in any way.

Is there a free version of Unity to support that?

As long as you stay under the profit threshold of Unity Pro, you can use Unity Personal as much as you want. Since you don’t publish, there is no profit, so just use Personal.