Safe TinyOS
What is Safe TinyOS?
It is an alternate toolchain for TinyOS 2 that uses the Deputy compiler to enforce type and memory safety at run time. Safety is useful for trapping pointer and array errors before they cause nasty consequences.
The SenSys2007 paper and slides can be found at: Efficient Memory Safety for TinyOS. Look here for more information about Deputy.
Safe Overview
An overview of Safe TinyOS can be found here: Safe TinyOS.
In particular, if you are trying to figure out the meaning behind Deputy modifiers, (such as "ONE", "ONE_NOK", and the like), you should look at section "Understanding Safe Code".