Optiboot is a project mainly written in C and JAVA, it's free.
Optimised bootloader for Arduino (and other Atmel AVR boards)
Optiboot is an optimised bootloader for Arduino.
It implements the STK500 upload protocol, so application code can be flashed over a serial port using Avrdude or the Arduino IDE.
Optiboot is very small (512 bytes) and has lots of optimisations to speed up the flashing workflow including Erase-while-communicating, high baud rates (115200 baud) and prompt bootloader exits.