This tip was copied and updated from:
https://discussions.apple.com/docs/DOC-2295#ROSETTALION for easier access to this information
First off if you have a Mac which shipped with 10.6.8 or earlier, you can restore 10.6 to a separate partition (has directions for making a partition), or external hard drive or flash drive if you need to keep running PowerPC applications. You will need the original installer discs, or if your Mac is older than March 15, 2010, you can use the 10.6.3 retail disc available on the Mac Online Store. For more on installing 10.6, see this tip. Backup your data before making a partition.
The following explains options if your Mac was released after Mac OS X 10.7's release.
Note before going through this process, also consider
https://discussions.apple.com/docs/DOC-6941 about various Office alternative software or
https://discussions.apple.com/docs/DOC-2741 installing Windows on your Mac.
Special instructions for those who have purchased Mac models that do not support Rosetta:
Rosetta is the application that is optional in Mac OS X 10.6.8 and earlier that allows applications made for Macs
that predate 2006 that run on Mac OS X to be run on Macs that started coming out in 2006 with the Intel CPU. Go to Apple menu ->
About This Mac to determine if you have a G3, G4, G5, or Intel CPU.
If it is Intel CPU, open your System Profiler application and read the model identifier to determine if you might need 10.6.8 Server (and can't run 10.6 Client) to be able to run Rosetta. These Macs are the ones that need it to be able to run Rosetta:
MacBook Pro 9,x and higher
Mac Pro EMC# 2629, and Mac Pro 6,x and later
Mac Mini 5,x and later
iMac 12,1 i3 (EMC 2496 on foot, MC978LL/A), iMac 13,1 and later
MacBook Air 4,x and later
Note: Older MacBooks without the "Air" or "Pro" moniker that are older than the one with the USB-C port can run 10.6.8 client, and don't need Server.
To tell the difference between USB-C and USB 2 see these images:
To identify your Mac read this tip:
Windows and Linux operating systems are not affected by these instructions. However, you can still run PPC applications using Snow Leopard and Rosetta by intalling Snow Leopard Server as a virtual machine using Parallels. This is not an exercise for the truly inexperienced user, but it is completely doable provided you are willing to spend some money and some time. A similar tip that explains these instructions, is https://discussions.apple.com/docs/DOC-5541
The System Profiler application lets you quickly determine if you have PowerPC (PPC) applications (click on image to enlarge):
Note the triangle to the left of Software has to be pointed down for the Applications to become visible.
Note the right hand side of the the Applications listing when selected says if you have PowerPC, Classic, Intel, or Universal.
PowerPC & Classic indicate PowerPC only. Classic indicates it only runs on a PowerPC with Mac OS 9 running in the Classic environment
or booting into Mac OS 9.
Apple Store online no longer carries Mac OS X 10.6 Server. Several third party resellers may still have it.
The product identification in the U.S. is MC588Z/A and it may differ by country.
For complete instructions on what to do see. Although the instructions are keyed to Parallels 7, you should instead use the latest version [sic] Parallels 8. (This information was contributed by user MlchaelLAX.)
Note: Check with Parallels if this is possible with newer versions of Parallels. Version 9 is out as of creation of this new tip. This has been successfully tested under Mac OS X 10.11.2 and every system between 10.7 and 10.11.2.