given certain means..
With this you can make test circuits, bash out an idea, show friends cool things that it can do. and so on.
You could probably make it usable with any computer with a serial port (or usb) with the right cable (depending on the board).
This is my entry for the Pocket Sized contest.
For my version I will be using a homebrew board of mine. it has TTL header pins, reset, power LED, digital pins and analogue pins, and a power rail. it has a 9v battery connector on it and the 7805 regulator is protected from power feedback but a diode, so there is no problem with powering it via another 3-5v source. But the board making isn't a part of this ible, so I wont be talking about its construction, (that's here: www.instructables.com/id/Compact-Protoboard-Arduino-type-thing-yea/).
On this board I will have loaded Bitlash ( a bit-bashing program and libs from ( http://bitlash.net/ ) that allows you to control the board and its pins (also its eprom) from any serial terminal interface. This makes it a little easier to try things out directly on the board instead of using the Arduino IDE software, and also means you don't have to carry that too.