Is there a P2P Networking client for mac? *NOT FOR ILLEGAL*

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Hi, my Dad's work is switching to a mac.  He wants to know if there is a P2P Networking client so that he can share files over the network (to do with work).  I know Limewire was originally going to be used for this purpose, but people hijacked it and use it for illegal now.  (I am not sure if Limewire is safe any more.)

Are there any 'good' *free* P2P Networking apps for mac.  I am not sure if Transmission can do it or not, or if this is just an *illegal* app.

What I am basically saying is 'Is there a way my dad and his work share work-related-files over his network (on macs)?'

Many thanks in advance.