This is a project that is based on Sanguinololu. The ATmega644P has been replaced with an Atmel AT90USB1286 MCU. This Microcontroller has on-chip USB, removing the need for the FTDI USB UART. All of the through hole resistors and capacitors have been replaced with 0805 SMT components (as of Ver 0.1). Like the Sanguinololu the Teensylu has expansion headers supporting I2C, SPI, UART, and ADC pins. All extra I/O ports of the AT90USB have been broken out to headers for prototyping.
The Teensylu adds new features like enable pins for eash motor (to save power), and a 4th stop called E-Stop to be used as an emergency stop, or extruder stop (to be added in firmware).