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.
HC-SR04 Ultrasonic Arduino Library is specifically for the HC-SR04 ultrasonic sensor. It features timing, metric conversion, and standard deviation methods, plus a few support methods. It is written in C++ to conserve the namespace. The conversion formula can be easily modified to optimize the accuracy of conversion at different distances for inches and centimeters. Multiple buffers of different lengths can be created for determining standard deviation.