I am surprised I haven't blogged about this before...
Interest free lending is often misunderstood - and it is assumed that there is no return to the lender, so it must be a waste of time, subsidised or bogus in some other way. However, this is not the case.
Interest free lending means the lender is rewarded in a way other than with interest.
The best set-up I have come across is Jak Bank - the principle is that you can borrow money for a period, but in return you must lend money for a period.
So you may deposit £100 for six months - and this will give you 600 borrowing credits (less a little for admin) which entitles you borrow anything from £1 for 600 months through to £600 for one month.
If you have established a good savings record, you may borrow beyond your earned credits - of course this is subject to some risk/trust etc but that is true of all life - however as loans should not be for speculating, it would be expected that they would mostly be secured on some asset in case of default.
This is effectively giving you a 'time shift' to manage your cash flow, and no one is taking profit, just covering costs. What is not to like?