One interesting use of an Arduino or compatible board is to act as a bridge between a personal computer and hardware that otherwise couldn't be directly connected to it, from LEDs to stepper motors, actuators and other devices. You can of course create simple control systems using the Serial Monitor with text-based controls, however there are several options.
One of these has been demonstrated by Ritik Bhardwaj who uses a C# application running on a Windows-based computer whose example has a neat GUI to control LEDs connected to the Arduino's digital output. The C# code sends serial text commands out via the USB port, which are then interpreted by the Arduino and acted upon. You can see this in action through the following video:
An interesting framework for further PC-based Arduino control. You can download the code and learn more from Ritik's project page. And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.
If you're interested in experimenting with LEDs as demonstrated above, we're offering large and bright 8mm diameter RGB LEDs:
They're in the common-anode format and look great when lit up. Ideal for colour-mixing and creating displays of all sorts. For more information and to order, visit the product page.