X11 for Mac OS X by Apple. Rootless, directly integrated and supposed to use Quartz. Hmm. The question is, does it already run on 10.1.5, or only from 10.2 onwards? Could be interesting, XDarwin is painfully slow and despite Oroborsx not really integrated. And occasionally I do need an X-Server after all, especially when I tunnel to my servers at the office.
First installation attempt failed anyway, the updater starts, but it won't unpack the file. Nothing, nada. No response. Strange. Maybe someone with 10.2 could test that?