I was wondering if I could use a display connected to another machine (Linux Mint XFCE) to extend my OSX desktop. Is this possible, and if so, how?
I am not aware of any Linux software that can do that, though there is some commercial OSX and Win software that enables you to use a screen as a second screen for OSX (over the network): http://avatron.com/apps/air-display#downloads
If you are running dualboot Linux/Win this maybe an option.
I use it with my MBP. The connection is fast enough for office, mail, browsing, etc.