I found this site I want to share with you.
Arduino Uno vs BeagleBone vs Raspberry Pi

Here's a brief summary:
All three are very small single board  computers you round fit in a beer mug. (Without the beer, of course.)

Arduino Uno is maybe the most popular at a price that is less that the parts alone if you went out and got the components off the self. It can be called a 'micro-controller' rather that a computer. It is slow and does mundane talks using  several I/O Ines. Requires. knowledge of C or related language.

Raspberry Pi is a better choice it you want to play with a small box that acts more like a very small computer. It has  TV output and enough RAM to run a stripped-down version of Linux. Only cost a few dollars more. About $35.

BeagleBone is overpriced but has more stuff. Still, the TV output is not included in the standard package. 
Here is an image the represents the general size of all three.


For much more information, read the first  the link above.
Or do a Google search or the keywords:
Arduino Uno, BeagleBone, Raspberry Pi

Myself, I have of of the  Arduinos,  but so far have not found a use for it. I would make a home security system, but we have a good watchdog already.  I have read into them, but havent bought any of them. Mainly because I feel very limited in the application of them and have no application that needs one.

The nice thing about them is that they save electronic hobbyists from having to create an interface from scratch, you can simply use this as a place to start without having to reinvent the wheel and the price tag doesnt hurt the wallet for the Raspberry Pi etc.

The last project I had that needed controls and an interface was back in 1998 when I decided to use a computer to control 8 relays through Parallel port to make stuff trigger in my yard that were driven off of the relays for a halloween setup. I had a strobe that was controlled on one of them with the PC speaker making thunder and other scary sounds etc, and had solenoids that would fire and make loud pop noises by home made fake coffins, skulls that had jaws that would open up quickly and the pc speaker would make a scream etc and an off balance motor in a dummy that would shake that was suspended etc. I also drilled small holes through some candles and ran fishing LINE through them  to suspend them in the air and had a few of them lit in which people would walk up to them and see that they didnt have a base and LOOKED like they were floating in mid air. The fishing line was strung between house and a tree. And with the night that one night being very still air I was able to light candles and have them lit and appeared to be floating etc suspended by the fishing line.

This was back when i had plenty of time on my hands and some money to spend on this stuff... now days i have not much time and I cant see wasting the money, but also in my area there are no more trick or treaters, all the kids now go to a fire house where there is a big community event etc and so halloween is dead in my area so no sense going all out when all the kids hit 1 event location and then go home after that. 

Here is that relay controller that was through parallel port: http://www.electronics123.com/kits-and-modules/computers/PC-Printer-Port-Relay-Board-kit-version-2.html

Looks like its still available 

Quote

Do you have an old PC lying around the house which absolutely no one wants? Then you can convert it into a dedicated controller. Communicate with the real world via the parallel printer port on your PC. Simply connect printer cable from computer to Centronics CONNECTOR on relay board. There are 8 relays each capable of switching 12VDC/10A or 240VAC/5A. Each relay has an LED to indicate when it is operated. We provide two sets of COMPLETE, stand-alone software to control the relays: one works under DOS so you can write your own batch files to control individual relays, the other under Windows 3.1. Needs 12VDC center positive 2.5mm power supply. PCB Size 6.75" x 2.75" (version 2) (CPS74)