BeOS was initially available only on a dedicated machine called BeBox. PowerMac and Intel releases followed, with R3 being the first Intel version (quickly replaced by R3.1). This is similar to NeXTSTEP, which started on NeXT computers. The first version of Intel processors was also 3.0.
Contemporary Mac OS X has more in common with NeXTSTEP than with classic Mac OS. When it was obvious that classic Mac OS design has limitation which cannot be overcome, and after several failed internal replacement projects at Apple (including the infamous Copland), the company started looking outside. When it was almost certain that BeOS will serve as a framework for the new OS, Apple surprised everyone by buying out NeXT, Inc., and using their operating system. BeOS was allegedly too limited (it couldn’t even print!) and too expensive. OS/2 and Windows NT were also considered alternatives, as both had PowerPC versions at the time.
NeXTSTEP 1.0 has been licensed to IBM, who ported it to AIX architecture. However, it took so long, that by the time the project was finished, NeXTSTEP 2.0 for NeXT hardware was ready. Since the company wanted more money for a new 2.0 license, and there was no obvious benefits, IBM lost interest in NeXTSTEP.