Somebody took a Model M and put upside-down Topres in it.
It's a buckling rubber sleeve. Similar to the M4 in my sig. The idea is it provides a more stable key press. Some people like it, some hate it.
I'm kinda more into Scissor Switches instead to stabilize the keypresses and yet give tactile feedback. Plus they can be much smaller.
IBM M4 is the second one down.Show Image(http://farm6.static.flickr.com/5206/5357080253_85656c54e3_z.jpg)
The buckling rubber sleeve keyboards that I'm most familiar with are the old KeyTronic keyboards. They're considered one of the better rubber dome keyboards, but still "ordinary" compared to mechanical switch keyboards.
This is also a vintage type of keyboard - it was only around at the time of the early Model M keyboards. It will have sturdy construction compared to modern keyboards, and probably sold for around $100 new if not more.
It's a decent keyboard, well worth keeping.
Mitsumi made also most of the keyboards with similar-looking switches for the Commodore Amiga computers, but I am not sure about which Amiga keyboards these are. I think that they were for the 3000 and 4000.
The keyboards in my Amiga 500 and 1200 have linear feel, so they must have had coiled springs instead of rubber sleeves.