In order for you to play Crawl on macOS with minimal graphics settings, your computer must meet the following requirements
Operating System:
Mac OS X 10.8 or later
Processor (CPU):
2.8 GHz Intel Core 2 Duo or equivalent
Memory (RAM):
2 GB RAM
Graphics Card:
OpenGL 3.2+ support (2.1 with ARB extensions acceptable)
Storage:
500 MB available space