C shrouding code?

[bill]

I've been asked to find out information about programs that
obfuscate C code. I can use either freely distributable or
commercial code, source or binary. If binary, it needs to run on
any kind of Sun or under MS-DOS.

If anyone has any suggestions about or experience with these 
things, I'd like to hear about it. Please respond via e-mail, 
since I don't read this newsgroup any more. I will summarize the 
answers I get if there is any interest.