OpenBSD/sun3 used to run on the Motorola 68020-based Sun3 computers, except for the 3/E flavour and the 3/50.
The OpenBSD/sun3 port was discontinued after the 2.9 release.
The source code is still available in the CVS Attic, and code can be found in NetBSD as well.
The Sun3 port of OpenBSD was derived from the NetBSD/sun3 port, when the sun3 and sun3x ports were still different entities. Noone showed much interest in OpenBSD/sun3 for a while, although the code was mostly kept in sync with NetBSD.
Eventually, Kenneth Stailey started working on the port, but since he was living in the USA, he could not export a release he would have built, so he lost interest working on this port.
Early 2000, Miod Vallat attempted to bring the port back in shape, making the code compile again, and devising completely new installation media. The port even shipped with complete X Window System client and utilities, although there was no working X server.
The port lived for a few releases, but unfortunately hardware problems and lack of time conspired to prevent catching up with NetBSD on code, and the sun3 code was not ready for the switch from the old Mach virtual memory system to uvm, and missed the 3.0 release, hoping that the code would be fixed in time for the 3.1 release. Unfortunately, this has not been the case, and eventually it was decided to remove the code from the tree.
The last supported OpenBSD/sun3 release was OpenBSD 2.9.