Sharing Sega Controllers

I would like to know what options in hardware exists for sharing controllers between one system and another.

I have a fairly common adaptor for dreamcast which allows one to use saturn pads, playstation pads, and ps2 keyboards. It works well.

I want to know what other adaptors were available for using sega controllers on other systems or vice-versa.

In particular, I am interested in finding an adaptor for using Genesis pads on an SNES. Both systems existed at the same time. It seems to me that many third party controllers must have existed. I found a suspicious one in korea, a pad the had both GEN and SNES cable extensions, but it was expensive and I suspected it was a "tourist special" because I wouldn't be able to test it before returning home.

1. Does anyone have in possession such a pad or adaptor to play SNES with a GEN pad?

2. What other cross platform joypads and adaptors are you aware of?
but I SAW one... I didn't buy it because i thought either it would not really work or that I could find it again elsewhere.

When I looked in my old electronic game magazines, I saw some table top arcade style joysticks claiming to be for both systems. If they exist, someone on this board must own it. I pretty much rely on the fact: if no one on SX board knows about it, it didn't relly exist.