Hi Alberto
The uTasker project contains FreeRTOS solutions (requiring no porting).
See the following with KL26Z FreeRTOS UART and USB-CDC operation:
http://www.utasker.com/kinetis/FRDM-KL26Z.html#FreeRTOS
Builds with CodeWarrior, KDS, MCUXpresso, IAR, Keil, Rowley Crossworks, CooCox, Green Hills, Atollic, GCC make file, S32 Design Studio.
Regards
Mark
Complete KL26 solutions, training and support:http://www.utasker.com/kinetis.html
Kinetis KL26:
http://www.utasker.com/kinetis/FRDM-KL26Z.html
http://www.utasker.com/kinetis/TEENSY_LC.html