I'd like to use the `ScrewTurn Wiki` in our company for an intern documentation system. I'm litle bit confused about the licencing. 

ScrewTurn Wiki is released under GPL license, which is an open source licence, but they have also a comercial `Internal Usage License`. 

So should I buy the licence or can I use the open source license in my company ? We won't make any changes,ressel it or anything. We just want to install in on our internall web server and share some content between colleagues.