Thanks for the advice Raxx,
Anim8or does run on Windows 8.1 in VirtualBox, but the performance is somewhat limited due to sharing of system resources, etc. I might try Parallels at some point in the future but for now I have set up a dual-boot configuration with Bootcamp. The trouble with this solution is that I won't be able to switch between Windows and Mac applications without rebooting. I wish there was a way to actually port Anim8or to Mac. A few years ago, I managed to run Anim8or in Ubuntu using Wine. I thought that it might also work on the Mac, but no luck; Anim8or starts, but then crashes immediately.