Thanks benseven; in case it wasn’t clear, I am interested in running the game natively,
that is, without a layer of emulation. I am looking for games that will not drain
the battery of a Macbook Air too quickly, not to mention the heat.
But because of the PPC -> Intel transition,
the usual trick of going back in time does not work for many games.
“PPC-only” in my question means that only a PowerPC binary is provided for the engine
in the Doomsday package that I found. It does run in Rosetta, only it uses as
much resources as a more recent game.
I may have used the wrong package, however, as I just found that this one
http://sourceforge.net/project/downloading.php?group_id=74815&use_mirror=dfn&filename=deng-1.9.0-beta5.1-universal2.dmg&4839178
does provide universal binaries for the engine and not just the launcher.
The “wrong” one is still floating around, and as I said initially, it looks
universal but it isn’t.
The universal version of Doomsday Engine runs smoothly enough with the default settings
on a 1st gen Macbook Air capped at 800MHz. I will take a look at the settings,
but for someone who is only interested in Doom, PrBoom (currently 2.5.0) is the simplest
choice.