There is Sigma Photo Pro 2.1 for Mac OS 9:
https://web.archive.org/web/20060909082445/http://www.sigma-photo.co.jp/english/support/soft/s_vol21_m.htmWith that version you can "darkroom" X3F-Raws (SD raws) to Tiffs, but only raws from Sigma SD9 and SD10 cameras, it also can preview SD14 raws, but crash to edit.
I think that SD14 support comes with version 2.2. And I think version 2.3 is last version for Mac OS 9.
And these version was short time available for free between May 2007-June 2008, but needed login with serial number of camera and that is reason that you cannot find it in archive.org.