The odds are that every computer keyboard you've touched uses digital switches. That is, they're either on, or they're off. PC hardware manufacturer Cooler Master is working on a keyboard with analog input, and it's on Kickstarter right now. The ControlPad is a small board with 24 keys, each one of them capable of full analog input, and it's not a complete ground-up redesign of standard keyboard switches.
The ControlPad has 23 single unit keycaps in an ortho layout (i.e. not staggered). At the bottom right, there's a single 2u keycap. These are all programmable, but you're probably supposed to use the 2u as a spacebar. Cooler Master is pitching this as a gaming device, which makes sense. Analog input offers more control in certain situations than a standard key.
When you play a game with a controller, you have analog sticks. You nudge the stick a little, and you move slowly. Push it all the way, and you go faster. A regular keyboard switch is just on or off; stopped or running at full speed. With analog input, you can press a key just a bit to move slowly.
I've used an analog keyboard in the past, but that device (the Wooting One) was designed with special optical switches that wouldn't work in a standard board. The ControlPad uses your choice of Gateron or Cherry Red switches—they're light and linear, which makes sense in this case. As you press, the ControlPad can output a signal that indicates how far the switch has been pushed, a technology known as "Aimpad."