XF 1.5 Clone Forum For Development

I remember seeing a link to this somewhere but since I don't know the lingo I don't know what to search for. How does one set up a copy of one's forum so that one can make changes to it without affecting the original?

Also, is it possible to give others access to this forum somehow? I have some volunteers who are willing to assist with coding and design but don't want to give them access to main forum immediately for obvious reasons, so I'd like to have a little playground for them to develop on independent of the forum proper.

Thank you for your time!