It depends on the EULA that the software came with. Some software is OEM which means it's only licensed for the machine it was sold with vs a full license which you're usually entitled to one installation on one computer (this you could uninstall and install on another computer and still be compliant).
I'm not sure how Apple does their licensing, perhaps their website would have that somewhere? Some companies do allow you to install in more than one place but it's usually limited and not very often since they'd rather sell you a copy but ya never know without reading it.
Unrelated bought a game (Sacred) because they allow you to install it on up to 4 systems on one license enabling us to have a small lan party without a huge cost. Norton pro also had a version that at the time would allow you to install it on 2 computers.
Most OSes however probably aren't too friendly for multiple copies but I'm not aware of any OS other than Windows that tries to check when doing updates, etc.
