Apple rewrote much of the OS in 64-bit, introduced Grand Central Dispatch for multi-core optimization, and reduced the OS's disk footprint by nearly 7GB compared to Leopard.
For modern tasks, Snow Leopard is obsolete. Use only in isolated, offline environments. snow leopard iso
It brought native Exchange support to Mail, iCal, and Address Book, bridging the gap for enterprise users. How to Get a Snow Leopard ISO Apple rewrote much of the OS in 64-bit,