Knew a guy in his his forties who wanted to work for an ad agency. Convinced them to use him for free for a while as a test and they wound up hiring him. YMMV.
Only an asshole company would do this to a future employee. And only an asshole would allow themselves to be exploited like this.
Guys: work on contract. Get paid. Your lack of self-esteem affects everyone else in the workforce trying to earn a living. Don’t sell yourself--or your peers--short.
1) They can't afford to, so probably aren't a very successful business.
2) They want to keep out the people who literally could not afford to live under this arrangement. (Disproportionately non-white, female, etc.).
3) You'll be of even less value to them than the minimum wage (so probably wouldn't be doing anything worthwhile/educational).
Don't take an unpaid internship, even if you can afford it. It perpetuates a terrible idea.