win32asm

PELock - is an application that allows you to protect Windows executable files (so called exe-protector). Besides that, PELock allows easy creation of application of evaluation-demo type, which use license key system.

Obfuscator is a tool to modify x86 assembler source code in this way to make an analysis of compiled code very difficult.

It is an unusual tool and the target audience is quite small, but if you're writing assembler code and you want to protect your work from decompilation or just to make it as hard as it's possible to analyze, you might want to try it.