Personally, I'm a huge fan of the old NTI KVMs. The pre-USB NTI KVMs support Sun, PS2, and ADB keyboard/mouse, including translation between each. There doesn't seem to be a whole lot of information about them online, so I put up what I figured out on my Old NTI KVMs page.
You can use either a Sun, PS2, or ADB keyboard & mouse, and the systems can be any combination of the above.
The KVMs are readily found on ebay, and sometimes go for fairly cheap. I've gotten a couple 8 port systems for ~$20 in the past, sometimes including shipping. I'm currently using a 2x16 matrix and a 4x32 matrix (meaning 2 or 4 keyboards/monitors can connect to any of up to 16 or 32 connected systems).
The KVMs support daisy chaining, so you can chain the KVMs together to get more ports if you want, and the KVMs are aware of each other so you can switch to any port on any of the chained KVMs from the same keyboard.
The only catch is cabling. The NTI KVMs natively use a Sun connector and you need appropriate cables to convert between that and PS2 and ADB connectors. This MKTINT-1 cable from kvm-switches-online works fine. It is advertised for plugging a keyboard into the KVM, but it works perfectly fine for systems, just keep in mind the ADB side is female and you'll need a male/male cable to plug it into systems. They used to sell varying lengths of the male/male Sun to ADB cabling, but that was discontinued not too long ago.
I've included some cabling pinout information, key mappings, and what the dip switches mean on my linked page.
You can use either a Sun, PS2, or ADB keyboard & mouse, and the systems can be any combination of the above.
The KVMs are readily found on ebay, and sometimes go for fairly cheap. I've gotten a couple 8 port systems for ~$20 in the past, sometimes including shipping. I'm currently using a 2x16 matrix and a 4x32 matrix (meaning 2 or 4 keyboards/monitors can connect to any of up to 16 or 32 connected systems).
The KVMs support daisy chaining, so you can chain the KVMs together to get more ports if you want, and the KVMs are aware of each other so you can switch to any port on any of the chained KVMs from the same keyboard.
The only catch is cabling. The NTI KVMs natively use a Sun connector and you need appropriate cables to convert between that and PS2 and ADB connectors. This MKTINT-1 cable from kvm-switches-online works fine. It is advertised for plugging a keyboard into the KVM, but it works perfectly fine for systems, just keep in mind the ADB side is female and you'll need a male/male cable to plug it into systems. They used to sell varying lengths of the male/male Sun to ADB cabling, but that was discontinued not too long ago.
I've included some cabling pinout information, key mappings, and what the dip switches mean on my linked page.