Lab Tick is an app that sits in your Menu Bar and allows you to manually control your keyboard backlight—even when the ambient light sensors (ALS) detect a light source—intended for use back when macOS didn’t include the option in pre-baked System Preferences and Control Centre.
It is a Universal Binary app, compatible with both PowerPC and Intel Macs, and can run on Aluminium PowerBook G4s (15" & 17" versions) all the way up to a range of Intel MacBook Pros.
It supports Tiger (10.4), Leopard (10.5), Snow Leopard (10.6), and possibly newer macOS versions (Lion 10.7 & above) with some tweaking of the info.plist.
Unfortunately, there are no newer updates past Snow Leopard (10.6) due to this being abandonware.
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Architecture 

OSX Universal Binary
System Requirements 
From Mac OS 10.4
Compatibility notes 
PowerPC G4, G5 & Intel - Starting from macOSX Tiger.
Emulating this? It could probably run under:
QEMU