Is there a Mac equivalent of DOSBox?
A good way to run classic Mac OS 9 applications on modern computers is to run the SheepShaver Emulator. I'm assuming that since your mac says the Classic Environment is no longer supported, you are trying to run a Mac OS 9 or below app.

http://www.emaculation.com/doku.php/sheepshaver_mac_os_x_setup

ROM files and classic disc images are easy enough to find online, but I won't link you any just in case it is against copyright regulations.