This is a very simple Makefile which knows how to build Arduino sketches. It defines the entire workflows for compiling code, flashing it to Arduino and even communicating through Serial monitor. You don't need to change anything in the Arduino sketches.
You can also find more [detailed instructions in this guide](http://hardwarefun.com/tutorials/compiling-arduino-sketches-using-makefile) or also checkout the sample makefiles inside the examples/ folder
If you are looking for ideas to work on, then check out the following TODO items or the [issue tracker](https://github.com/sudar/Arduino-Makefile/issues/).
- Since it doesn't do any pre processing like Arduino IDE, you have to declare all methods before you use them ([issue #59](https://github.com/sudar/Arduino-Makefile/issues/59))
- More than one .ino or .pde file is not supported yet ([issue #49](https://github.com/sudar/Arduino-Makefile/issues/49))
- When you compile for the first time, it builds all libs inside Arduino directory even if it is not needed. But while linking only the relevant files are linked. ([issue #29](https://github.com/sudar/Arduino-Makefile/issues/29)). Even Arduino IDE does the same thing though.
- It's not a derivative of this, but Alan Burlison has written a [similar thing](http://bleaklow.com/2010/06/04/a_makefile_for_arduino_sketches.html).
- Alan's Makefile was used in a [Pragmatic Programmer's article](http://pragprog.com/magazines/2011-04/advanced-arduino-hacking).
- Rei Vilo wrote to tell me that he's using the Makefile ina Xcode 4 template called [embedXcode](http://embedxcode.weebly.com/). Apparently it supports many platforms and boards, including AVR-based Arduino, AVR-based Wiring, PIC32-based chipKIT, MSP430-based LaunchPad and ARM3-based Maple.