Snow Leopard was the cutoff.
Leopard was the last version with PPC support.
Snow Leopard was a "more efficient, improved" Leopard. One of the "more efficient" elements was dumping all PPC support, including the emulation layer for Intel machines.
Lion uses Snow Leopard as a base and incorporates a bunch of iOS features.
Snow Leopard supports PPC applications. Lion is the first OS not to run PPC applications. Snow Leopard was, however, the first version to not install on a PPC machine. It goes like this:
Tiger: Installs on PPC, Installs on Intel, Runs OS9 Applications, Runs PPC Applications
Leopard: Installs on PPC, Installs on Intel, Does Not Run OS9 Applications, Runs PPC Applications
Snow Leopard: Does Not Install on PPC, Installs on Intel, Does Not Run OS9 Applications, Runs PPC Applications
Lion: Does Not Install on PPC, Installs on Intel, Does Not Run OS9 Applications, Does Not Run PPC Applications
yes I know, but there should always be an option. I used a lot of PPC apps even after the migration to intel.
The problem is that in order for Rosetta (the emulation layer) to work properly, the system requires PowerPC libraries and system files to be installed as well. That means that Apple must not only maintain an Intel version of their OS, but also maintain a PowerPC version, even though they haven't made PowerPC hardware for over half a decade. That's a lot of work, and everything has an Intel binary nowadays anyway. When Lion was released, the only notable piece of software that didn't have an Intel build was Quicken, and Intuit finally updated it now. When I upgraded to Lion the only thing that I had on my system that wouldn't run is the SheepShaver Emulator's Configuration GUI.
I.M. Weasel wrote:
It was made with the 10.2.8 devkit, which was before Xcode. At the moment I don't have access to a Mac.. and i'm not sure which OS/devkit/mac I could use to get the best forward & backward compatibility. Although I am interested in keeping it at least running in the newest version, even if no additions are planned. Not sure of a timetable right now.
If you don't mind giving me the source code, I could probably get it running, and I have a PowerBook G4, 32-bit MacBook, and MacBook Pro. I can test on Jaguar/PPC, Panther/PPC, Tiger/PPC-Intel, Leopard/PPC-Intel, Snow Leopard/Intel, and Lion/Intel. Modern Xcode probably won't let you build for anything earlier than Tiger, though.