The mbed is a tool for rapid prototyping with microcontrollers using the beefy LPC1768 ARM Cortex M3 chip. While it looks like a classic breadboard-friendly breakout board, this dev board has a few tricks up its sleeve. First of all, underneath the PCB is a second LPC chip which acts as the programmer: when plugging into a USB port the mbed shows up as a flash drive and programs can be 'dragged' onto it for uploading. This makes it easy to program without an external device, and makes bricking impossible. There's also a bunch of indicator LEDs, and a little flash storage chip as well.
Writing code for the mbed is a little different than you may be used to. Instead of downloading the IDE and installing it locally, the user must instead visit the http://mbed.org website and use the web-based 'cloud' programming system. Since the board is programmed via drag-n-drop, no software is installed. The good news is that it means its easy to work on anywhere you are just by logging on, and there's a vibrant social network sharing code on the mbed site. The bad news is that Internet access is required to work on a project.
New users can get started with mbed tools in 60 seconds, by plugging in an mbed microcontroller, going to the mbed.org website to sign up, and downloading and running a "Hello World!" binary just like saving to a USB flash drive. Compiling a first program takes only 60 seconds more; Launch the browser-based compiler, create a new template project, click 'compile' to build and download the binary - there is nothing to configure or install, and everything works on Windows, Mac, or Linux.
The mbed's core chip, the NXP LPC1768 features:
For more information, see the http://mbed.org website.