Capture was of course a Capture cartridge by Jason Ranheim.
Like other capture cartridges, when you press a button it will save the memory contents to disk. Which you can boot again later. This was a great way to by pass boot up copy protection.This is a SUPER RARE cartridge that usually sells for over $100.
There are now reproductions of this you can buy, just do a Google search.
Below is the one from my personal collection and a few screen shots.