The Teensy 2.0 is a complete USB-based microcontoller development system, in a very small footprint! All programming is done via the USB port. No special programmer is needed, only a standard "Mini-B" USB cable and a PC or Macintosh with a USB port. This is the latest version, 2.0.
Comes with assembled Teensy board (ATmega32u4 with bootloader preinstalled) and header to allow easy breadboarding. We suggest using AVR-gcc (like WinAVR) with the LUFA library or 'Teensyduino' Be sure to check out the multiple resources available at PJRC! We also stock a atmega32u4 breakout board, read more here including why you'd want to use a Teensy or this board.