Whether or not it's an illegal security offering, I'm not entirely sure because I don't fully understand the law. However, a hypothetical example of one purported not to be illegal would be something like crowdfunding a game. You sell tokens that will be redeemed for a copy of the game when it is finished. This would allow people who change their mind half way through to freely sell their game token to someone else who wants to buy the game (presumably at a loss since otherwise the other person would just buy the game token from the developers). There are probably lots of places where you might get in trouble though. For example, if you increased the price of the token over time, then people might buy the initial token with the expectation that they will be able to sell it for a profit later, when the developer-bought token becomes more expensive. Especially if you state that the price will increase over time, I think you're going to be in trouble (but, like I said, I don't really understand that law).

I think such a scheme, if done carefully, might actually be useful. One of the problems with things like kickstarter is that you see the plan of what's going to be done, fund the project and then half way through you see that the plan has changed, or the delivery schedule has changed and you want out. There is no way to derisk your pre-purchase.

Having said that, I have seen no actual examples of ICOs that I think are legal.