Frog Lube. It smells minty and you can literally eat it.
Simple Green - as long as it's not used on aluminum. That's a pretty mild/gentle detergent.
If he is looking for greener and "Safer" chemicals I would have to say +1 on the Frog Lube.
I have a tube that I bought back when it was the greatest thing to hit the gun industry. Did two guns with it and haven't touched it since. Not a fan when it is cold out so I have moved back to a simple synthetic motor oil.
I am going to start coating my carbon steel hunting knives with the Frog Lube though. It was mentioned in another post and I thought it was an awesome idea.
Is he wanting a cleaner or lubricant? (oh wait...I think Frog Lube is both it also improves accuracy, makes cleaning easier, less smoke, salt water proof, and could be the cure for cancer!)
Sorry...insert purple where suitable.