The Arduino hardware provides a very inexpensive basic development system and is ideal for learning assembly language or C programming.
Although it is possible to program arduino in assembler, there are more suitable environments for doing this than the Arduino IDE.
While you can program with assembler using the arduino environment, sort of....
For an inexpensive (around $50 US) introduction to assembly language programming some Arduino-type hardware, AVR Studio 4, and a USB programmer that uses the ISP interface is a good choice.
So i see linux, windows and mac os x... are bsd systems supported?