There was also the PPC615 in the mid-90s, done by IBM, which was socket-compatible with the Pentium, and could execute at least PPC32, PPC64, and x86_32 nativel

There was also the PPC615 in the mid-90s, done by IBM, which was socket-compatible with the Pentium, and could execute at least PPC32, PPC64, and x86_32 natively (I'm not clear on whether it supported x86_16): the decode step for x86_32, AIUI, essentially decoded it into PPC instructions. It was meant to be competitive with the Pentium in x86-mode, and could change between ISAs at the thread level, I believe. Ultimately it was scrapped as people in charge believed Intel were about to move away from IA-32 and the industry would follow to IA-64 with its IA-32 compatibility.