Stellar

sent! my username is xenadu

Thinking about this a bit more, there is one flaw with using it to track debts among a circle of friends, which is that any of those friends could then turn around and trade the USD-stellar I issued them to someone else, who doesn't realize that they shouldn't actually trust me for it. Using a fake currency as a proxy for USD would work here, but of course fake currencies have their own problem which is everyone has to invent a unique fake currency to avoid confusion.

Another solution would be to allow gateways to declare that their coins are only redeemable by a limited set of accounts. That way I can be a gateway and issue USD-stellar that everyone knows is worthless if it leaves the circle of friends. I could do this ad-hoc just by refusing to redeem any issued coins by someone outside the group, but as mentioned above that leaves open the possibility of people not realizing that these particular coins are worthless (outside the group). Of course, this also has the problem where someone may now look at their balance and see that they have $500 USD, but not realize that $50 of it is actually debt issued by me, because the software they're using doesn't distinguish restricted coins from others.

Perhaps the fake currency approach really is the best. This has the benefit of letting an extended group of friends trade around debt issued by people they're not actually direct friends with, but they trust transitively through a shared friend. If I decide to accept debt issued by Alice, and Alice refuses to pay up when I go to her, I can then talk to our shared friend (but hopefully Alice would agree that the debt I bought from Joan is still valid and pay up). The downside is, of course, that everyone has to be using the same centralized shared currency. And that won't scale past a small group of friends (if it did, it wouldn't be a fake currency anymore). Although if you have several smaller circles of friends each with their own currency, and there's overlap, they could decide to trust the other currency and treat it as equivalent to theirs. I guess this is a continuation of Stellar's philosophy that the trust is granted by the person accepting the coin, rather than being dictated in any fashion by the issuer.

Of course, all this is predicated on the fake debt-currency not spreading far. As you try to scale to larger groups of friends, it ultimately ends up being simpler just to switch to USD.

I guess the real challenge here is figuring out how to let Stellar wallet clients display contained balances in a way that doesn't confuse coins issued by generally-trusted gateways vs coins issued by small gateways that most users probably won't trust. If I can somehow either categorize myself as a gateway, or each gateway I trust, those categories could be used to display balances appropriately. This way I can categorize Alice, Joan, Bob, Fred, and Jane as debt-issuing friends, and they can issue USD, and I won't accidentally think I have $500 USD when I really have $450 USD and $50 friend-debt. This doesn't really solve the problem of trading debt to people who don't realize it's worthless, but I don't know if that's a legitimate worry.

You can indeed issue fake currencies. The only technical limitation is that currencies are (as it stands) limited to 3 letters.

Note that your friend would only be able to trade your fake currency to someone who is willing to trust you, so there's no obvious need to have more technical enforcement preventing trades.

Why isn't pre-mining viewed like VC-less VC?

That's assuming your gateway has stellar on hand to provide as conversion. Stripe is starting with 2% of the stellar, but (AFAIK) nobody else is starting with any significant chunk. If a gateway issues credit in exchange for real-world exchanges, I don't see why there's any expectation that they'll have stellar on-hand to use for the conversion, although perhaps they can use their real-world money to buy stellar from some other gateway.

I'm also wondering, since the amount of Stellar is capped (100 billion, right? Can this ever change?), and since 50% of Stellar is being distributed to people who sign up, it seems like a sizable portion of this Stellar will almost certainly immediately become unusable as people sign up, get their Stellar, and never come back.

Edit: Just found the bit where it says Stellar will be created at a rate of 1% annually. The fixed 100 billion cap I cited was based on earlier comments about Ripple's cap.