Mac OS X has always come bundled with a version of Emacs, I see a copy of a binary named emacs-20.7 on the OS X 10.0 installation CD. On a fully patched version Mac OS X 10.4 Tiger, the version of Emacs is 21.2.1, 22.1.1 on Leopard and on more recent versions of macOS since Catalina it has been replaced by mg.
I wondered what the most recent version of Emacs would run on Tiger. The Emacs for Mac OS X project maintained builds at some point and has copies to the most recent builds and impressively all their builds going back to 2009. Great, I fetched both the nightly and 24.5-1 build for Tiger and tried them, only to be presented with errors regarding _getrlimit$UNIX2003 symbol not being found when running the Emacs-powerpc-10_4 binary inside the Emacs.app. Double clicking on the Emacs icon attempts to launch the application and an icon appears on the dock before disappearing again. I left it there and started looking at building the most recent version which I could myself.
Support for OS X prior to 10.6 Snow Leopard was dropped with Emacs 25 which is why the most recent builds were of version 24.5. I managed to build 24.5 on Tiger without issue, running the result not so much. It turns out that 24.x to 25 was a turbulent time for OS X support in Emacs. My build of 24.5 would launch, a blank window would show, CPU usage would spike and eventually crash and disappear.
Same result for 24.4.
On 24.3 things things were a little more compact but same crashing behaviour after a short period.
The issue was apparently resolved in Emacs 25 but there’s more required than just this change for 24.5 as cherry picking It didn’t resolve the crashes and I didn’t investigate any further.
Emacs 23 was good. I had a working application on Tiger with 23.4.1.
I headed back to Emacs 24 and built 24.2, and that was good too. Currently, I’m stuck on that version and haven’t yet investigated where things broke on the road to 24.3. Emacs 24 introduced support for installing packages from a remote repository. Due to its age, its concept of handling encrypted connections via TLS wont work with newer versions of OpenSSL since it tries to invoke s_client with SSLv2 turned off which of course is no longer a supported feature. Another option is to use GnuTLS but I haven’t yet managed to build a new version of GnuTLS on Tiger to use with it since GnuTLS has grown another TLS requirement which requires a compiler with C11 support. This is not so much of an issue for connecting to Elpa, but Melpa requires HTTPS and given a recent version of OpenSSL and Emacs 24.2 built with a modified lisp/net/tls.el to drop -no_ssl2, it’s still not happy about something and will sit there for some time and fail. I sidestepped the issue for now by using a Melpa mirror which works via HTTP, and needed a couple of changes from from Emacs 25 to packages.el for version handling, otherwise it would fetch the repository metadata and fail due to an invalid version.
If you’re looking for a newer version of Emacs with GUI support to run on your PowerPC Mac, I’ve posted the binaries here. The binaries were built on OS X Tiger 10.4.11 PowerPC with ./configure --enable-ns-self-contained --with-ns and run tested on OS X Tiger & Leopard PowerPC. No idea if/when another build will be, but they’ll end up in /files/macosx-powerpc-emacs/ if I do.