To be a bit more specific, Mac OS X Rhapsody DR2 (1998) was the last x86 Mac OS build to ship until the x86 Developer Transition Kit shipped with Mac OS X Tiger 10.4.1 in 2005, and Rhapsody DR1 was the first, and only other, pre-Tiger x86 Mac OS release, though unreleased x86 ports of earlier, pre-NEXTSTEP Mac OS releases were demonstrated internally[1].

Additionally, NeXT shipped several x86 releases of NEXTSTEP and its successor OpenStep (NEXTSTEP 3.1–3.3, 1993–1995; OpenStep 4.0–4.2, 1996–1997) prior to the acquisition, all of which also run under virtualization with some effort — though I'd personally recommend the Previous emulator[2] for running older NEXTSTEP builds, as it runs reasonably fast on modern hardware and quite a bit of historically interesting NEXTSTEP software exists that was never released for versions of NEXTSTEP running on non-NeXT hardware (Mathematica 1.0, Lotus Improv, WordPerfect, and the original CERN WorldWideWeb browser come to mind, though source ports of the latter exist).

[1] https://en.wikipedia.org/wiki/Star_Trek_project

[2] https://www.nextcomputers.org/forums/index.php?topic=2642.17...