I booted a G4 Mac the other day, running 10.4.something. I was thrown back in time to a period where OS X was clearly their flagship software stack. Everything was coherent and cohesive - and shockingly - fast. I'd daily 10.4 again if it could operate on the modern internet comfortably!
Nevertheless, I also remember that in the 10.4 days, OS X had the reputation of being sluggish compared to Linux or even Windows (I guess it was Windows 7 at the time?). And it kinda was. Bouncing ball when launching an app.
