The Tinyserial library is a space-saving alternative to the Arduino software distribution's libraries for reading and writing characters and strings to the USART0 serial port on the Atmel ATmega168 and ATmega328p MCUs found on Arduino Diecimilla and Duemilanove boards. While the Arduino software distribution's libraries provide interrupt-driven serial I/O with far more features and support more MCUs, the Tinyserial library provides only the most basic polling-based serial I/O. However, the Tinyserial library uses far less Flash and SRAM, thereby giving you room to implement larger and more complicated applications on your boards. The Tinyserial library respects the GNU libc ABI, so you can call into it from C and C++ programs.
cduino is a microcontroller programming system that is like arduino but simpler. It allows experienced programmers to get a quick start programming and talking to a microcontroller. You should be up and talking to your arduino over the serial line in a matter of minutes. This is achieved using a very easy Makefile-based driver for the command line Atmel AVR programming tools, a library of C routines, and a series of lessons that introduce a variety of AVR subsystems.