mbed is quite popular on the FRDM-KL25Z board, and now two more Freescale Freedom boards have been added to the list. The FRDM-KL46Z and FRDM-KL05Z are now mbed enabled, with full details on the mbed.org website.
mbed is a really easy to use tool by ARM that provides a free online software and hardware development kit, and free online IDE, to quickly develop projects for mbed enabled development boards. Currently the FRDM-KL46Z, FRDM-KL25Z, and FRDM-KL05Z are mbed supported.