Don't know what a raspberryPi is, well sir you have not lived. It is THEE place to be these days if you like your tech and like to tinker even more. The raspberryPi helps to blur the lines of virtual and physical in a lovely blurry mess at a very affordable price. Learn to build, solder, make and adapt till the cows come home.
The raspberryPi is a small, cheap single board ARM computer. It comes as a bare PCB that can be hacked, adapted and moulded into anything from a games machine to a robot. They come is various sizes and various price ranges depending on what you need. Started from £4 and goign up to £40 pound, you can get a multicore ARM computer to meet your needs.
Whilst I am probably angering a lot of enthusiasts by doing this, I like to use them to build web servers, and yes, we are free to do what we want with them, so if you cant bare to read on, then don't, I do plan on using my last pi zero to do something more physical, at present my pi work is more server related.
The raspberryPi makes a perfect webserver, and even better when you combine it with the power of docker. You can either build and run as a simple single server, a more advanced managed group, or as an all out balls deep cluster. Whilst I have compiled to my hearts content in search of the ultimate system, I have found that the best and quickest (yes we want it all now) is to go hypriot, these guys are the shizzle. You can spend time messing around, building, compiling, seriously, these guys have done the boring stuff and got it nailed, just start with the hypriotOS and enjoy.
The balls deep cluster bad ass, build and manage a cluster of pi's with almost voodoo like automated goodness. This image that you can plonk on a microSD as easy as cracking a top off a bottle of suds will amaze you. You start the pi's up and they just find each other, configure each other, all you do is slap your docker images on there and they spread like butter or constrain to a single pi. Running the hypriotOS (raspbian (debian)) you get an up to date version of jessie, with an up to date version of docker and all associated tools.
Don't fancy balls deep, no worries, you can swarm the pi's manually if you wish (virgin routers suck a little so cluster labs messes with vlan on it), this blog post talks through some of the requirements and gives you a how to, to get you swarming pi's as a cluster and get some sweet docker goodness. Still not convinced you need to swarm your pis, no biggy, I manage a group of indvidual pis through proxies, gives me much greater control (as these pis have little ram and some images need much much more ram).