Freescale (now NXP Semiconductors) created the "Freedom" series of boards to support low-cost development for the Kinetis ARM-Cortex M series of low-power microcontrollers. The FRDM-KL25Z is one of the most popular boards, sporting a KL25Z128VLK4 ARM Cortex-M0+ ultra-low-power micro, with 128KB FLASH, USB, Touch slider, 3-axis mass accelerometer (MMA8451Q) and OpenSDA debug interface.
Freescale provide several excellent resources for getting this board up and running, including an introduction video and step-by-step instructions on seting up the software development environment. The easiest and probably best way to get things going is to download and install the Kinetis Software Development Kit (KSDK), along with the Kinetis Design Studio IDE (KDS), which is based on the Eclipse environment and the ARM GCC toolchain. Follow the external link to see these resources.