Share 'apps which require external hardware'

I am in need of information about Android applications which require external hardware to function. By this I mean things like the below.  Oscium (app + hardware) which lets an iPad be used as an oscilloscope http://oscium.com/ iPhone-attached geiger counter as in http://www.tuaw.com/2011/04/15/iphone-geiger-counter-would-benefit-japan-needs-kickstarter-lov/ Square for Android (credit card reade…