Amiga 3.5 and 3.9 were created by a German company back in 1999/2000 and require a 68020 or better processor.

https://en.wikipedia.org/wiki/AmigaOS#AmigaOS_3.5,_3.9

3.1.4 and 3.2 were created by Hyperion Entertainment. 3.1.4 and 3.2 by the looks of it support all the 68000 series processors and these as stated in the article are more recent.

They also were not developed by the same company. 3.5 and 3.9 were developed by Haage & Partner, 3.1.4 and 3.2 were developed by Hyperion Entertainment.

There's even an AmigaOS 4.0 from Hyperion which is PowerPC only.

For extra bonus points, there's MorphOS which is a heavily AmigaOS influenced OS. PowerPC only, runs on some of the older PPC Macs.

And there's also the open source AROS reimplementation of AmigaOS 3.1 (with a lot of extras).

(I'm sure I got a lot of details wrong, been years since I last did Amiga stuff.)