I got some friends who run really old OSX versions (pre snow leopard) and some things like Skype don't work anymore because the software refuses to work on such an old OS. Given that it is old slow hardware which OSX version to you think I should update them to. One is already a unibody 13" and the other is still running Tiger. I thought snow leopard but that is still quite old. What do you guys think? Yosemite gives my old 2010 15" troubles so I guess that would completely freeze such old hardware.