B2B Barter systems like the WIR in Switzerland and proprietary systems such as Bartercard and BX all have credit built in, and where you have a barter system with in-built credit, then the result is a monetary system.
The reason for the pervasive (multi billion Swiss Franc) success of the WIR in Switzerland is that all members have to give a charge on their property to secure against defaults (ie non payment of debit balances).
ie the WIR is property-backed.
No one has yet managed to extend these B2B systems to customers as well (B2C).
But this will happen, and when a simple piece of software (a "transaction engine") does appear (there are several candidates) all that will be necessary for a complete credit solution is a mutual guarantee backed by provisions made into a mutually owned default fund.
At that point we will have created a "Clearing Union" (as advocated by Keynes) and banks as credit intermediaries will have become obsolete.
Of course, they could still have a role as service providers managing the process of credit creation; setting guarantee limits; managing defaults and so on...all without putting their capital at risk by creating credit based upon it... "Any economic unit can emit money. The serious problem is to get it accepted" Hyman Minsky
