Kickstart 1.0 - 3.1: By Commodore. Actually 3.0 was "officially" last but 3.1 was ongoing work that got wrapped up well enough. I don't really remember if Commodore officially released 3.1 or if it was picked up from their corpse by someone.
HAAGE & PARTNER BRANCH:
AmigaOS 3.5-3.9: First post-3.1 versions from 1999-2000 (for Motorola 68020 and up rather than 68000 and up) by Haage & Partner. Main features a TCP/IP stack and a new GUI, a new GUI toolkit called ReAction, MPEG movie player, MP3 player, >4 GB disk partitioning support.
HYPERION POWER PC BRANCH:
AmigaOS 4.0-4.1: First PowerPC-only version. Main features memory virtualization, new GUI, integrated third-party graphics driver support, etc.
HYPERION "CLASSIC" BRANCH:
Now they returned to 3.1 BUT with 3.9 source code still on their hands. Trying to advance Kickstart from a new angle that allows support for all Amigas, even the 68000 (Amiga 500). This is NOT for PowerPC. AmigaOS 4 is for those systems but since that's basically a dead end in 2021, this is a more pragmatic move. I also find less "careless" and more conservative than 3.5+, focusing on kernel improvements rather than bolting on big third party tools and libraries. Basically more how I'd expect actual Commodore releases would look like.
AmigaOS 3.1.4: Backporting numerous features and lessons learnt from 3.9 and now available for all Amigas, that is including the MC68000. An important update for classic Amigas since it brings in particular support that makes interacting with modern hardware easier with larger hard drives, and I think it added MC68060 support too for accelerators and whatnot.
AmigaOS 3.2: A continuation of the 3.1.4 branch and now probably surpassing 3.9 in many areas.
Kickstart 1.0 - 3.1: By Commodore. Actually 3.0 was "officially" last but 3.1 was ongoing work that got wrapped up well enough. I don't really remember if Commodore officially released 3.1 or if it was picked up from their corpse by someone.
HAAGE & PARTNER BRANCH:
AmigaOS 3.5-3.9: First post-3.1 versions from 1999-2000 (for Motorola 68020 and up rather than 68000 and up) by Haage & Partner. Main features a TCP/IP stack and a new GUI, a new GUI toolkit called ReAction, MPEG movie player, MP3 player, >4 GB disk partitioning support.
HYPERION POWER PC BRANCH:
AmigaOS 4.0-4.1: First PowerPC-only version. Main features memory virtualization, new GUI, integrated third-party graphics driver support, etc.
HYPERION "CLASSIC" BRANCH:
Now they returned to 3.1 BUT with 3.9 source code still on their hands. Trying to advance Kickstart from a new angle that allows support for all Amigas, even the 68000 (Amiga 500). This is NOT for PowerPC. AmigaOS 4 is for those systems but since that's basically a dead end in 2021, this is a more pragmatic move. I also find less "careless" and more conservative than 3.5+, focusing on kernel improvements rather than bolting on big third party tools and libraries. Basically more how I'd expect actual Commodore releases would look like.
AmigaOS 3.1.4: Backporting numerous features and lessons learnt from 3.9 and now available for all Amigas, that is including the MC68000. An important update for classic Amigas since it brings in particular support that makes interacting with modern hardware easier with larger hard drives, and I think it added MC68060 support too for accelerators and whatnot.
AmigaOS 3.2: A continuation of the 3.1.4 branch and now probably surpassing 3.9 in many areas.
AmigaOS 3.x...?