That's the Native Instruments B4. It's a Hammond organ simulator program. You can play it via any keyboard that has MIDI and a computer with MIDI (or these days some keyboards have USB interfaces and you can plug them into the computer that way). Then when you set everything up right, you hit a note on the keyboard and the software (in this case, the B4) creates the sound and outputs it through your soundcard.
The B4 is the best Hammond simulator I've heard... that said, it still has a lot of things wrong with it... things that are not simulated at all or not correctly. I won't go into it here.
What's the point? Well, the program cost about $200 whereas a real Hammond and Leslie would set you back a couple of thousand... not to mention the upkeep. This is a cheap way to get a decent Hammond sound on your tracks. If it's part of a dense mix, you probably couldn't tell it's not real.
Also, if you have a powerful enough laptop, you could use this live. I know a cat that did just that. He had a MIDI keyboard and his laptop. It kicks the snot out of any of the current hardware organ simulators like the Korg CX3 and the Hammond-Suzuki XB2. The only crappy thing is not having real drawbars to pull but if you set up enough presets it probably wouldn't matter too much.
Almost all hardware synthesizers nowadays are dedicated, streamlined computers meant to produce sound... these programs use your existing computer to do the same thing. It's the WAVE OF THE FUTURE, as I keep telling Joe. Personal computers are infinitely upgradeable and cheap whereas hardware synths are neither. Software is the way to go!