什么是最近的裸机操作系统？

What are some tiny open source operating systems? I'm looking for something several orders of magnitude smaller than Puppy Linux, Feather Linux, DSL, etc. I want to run a command-line text editor and compiler; anything else is extraneous. I'm looking for a system I can take apart and acquire a fairly good understanding of the whole thing in a reasonable period of time. Bonus points for something that is portable and well-documented.What are some tiny open source operating system