One protocol. Many streets.

The general principle.

The plumbing of a peer-to-peer rental is small. A deposit posted by the renter and visible to both parties. An agreement that says what the rental is and when it ends. A receipt of both, written somewhere neither party controls. A small group of people who know the asset, on hand for the rare case when the first three are not enough.

That is four moving parts. They do not change when the asset changes. A bike, a drill, a washing-machine slot, a Lastenrad, a sublet, a cello — the contract holds money the same way for each, and the guild that hears a dispute is different in each case but constituted the same way. One protocol. Many streets.

The mistake the last fifteen years made was to build one app per asset class. An app for scooters. An app for short-stay rooms. An app for tools. Each one a marketplace with its own custodian, its own dispute team in another country, its own version of the same five primitives, none of them shared. DaiZen is the inversion. The primitives are shared. The local instances are not.

A way to think about scope.

What can be shared this way? More than the question suggests. A useful cut is along three axes — not as categories to fill, but as dimensions to feel.

By scale. Micro: the Tuesday-evening washing-machine slot in the Hinterhaus, fifty minutes long, deposit measured in coins. Meso: the drill for the weekend, deposit measured in the price of a new one. Macro: the apartment for the Erasmus semester, deposit measured in a month's rent. The plumbing does not change. The number on the deposit does.

By trust load. A bench in the courtyard, lent on a photo and a handshake, almost no deposit. A car for a weekend, where the deposit covers excess and the guild is on standby. A flat for four months, full ID, full deposit, a guild member walking through on arrival. The same contract holds them all; what changes is what the parties agreed before they signed.

By time horizon. One-off — the tile saw for the bathroom project. Recurring — the carpool to the same office park twice a week. Seasonal — the touring skis that live in a closet from April to December. Each shape calls for slightly different terms; none of them call for a different platform.

Three rooms, in more detail.

A car to Oerlikon.

A neighbour drives to the same office park twice a week. The car carries one person and three empty seats. The waste is obvious; the friction has always been the trust. A short ride is too small for a contract and too irregular for a payroll deduction. So the seats stay empty.

With a deposit-backed protocol the friction goes away. The driver posts the route. The passenger reserves the seat; the fare is held alongside a small deposit against a no-show. The car logs the drop; the fare clears at the other end; the deposit returns. Two people who already work in the same district have agreed on a price. No fleet, no surge, no platform commission.

A Tuesday slot in the Hinterhaus.

The shared washing machine is the smallest rental there is. The asset is fifty minutes of a machine the building already owns. The problem is not the machine; it is the no-show — the booked slot held by someone who never comes down to start the cycle, while two other tenants need a clean shirt for tomorrow.

A small deposit on the slot — a fraction of a franc, refunded when the cycle actually runs — turns a courtesy into a commitment. The machine reports the spin. The deposit clears. No neighbour has to send a passive-aggressive note in the stairwell. The mechanism that handles a thousand-franc bike rental handles a half-franc slot the same way, because half-franc and thousand-franc are just numbers in the same contract.

A flat in Wiedikon, for one semester.

An Erasmus year in Lisbon. The flat in Wiedikon sits empty from September to February. The owner wants a careful subletter; the subletter wants somewhere quiet to land for a winter. The classical version of this is a chain of trust intermediaries — an agency, an insurance product, a handover that has to happen in person on a date neither party chose.

With the protocol underneath, the chain shortens. A month's rent posts as deposit, held in a contract neither party can move. A member of the housing guild walks the flat at handover, notes the state, signs the report on-chain. Keys exchange directly. If a dispute arises in February, the guild has the walkthrough, the chats, the agreed terms, the deposit — everything it needs to decide. Without anyone in between taking a cut.

What the protocol provides.

Five primitives, composed differently for each room.

An asset registry — what is being shared, what state it is in, who owns it. A deposit-and-fee escrow — what the renter posts, what the owner is owed, when both clear. A device or evidence layer — the smart lock for a bike, the meter on a machine, the photo at handover, whatever the particular asset uses to prove it was used as agreed. A reputation record — carried by both parties across assets and across years, never owned by the platform. And the guild — the small body of practitioners that hears the rare hard case, with the first four already on the table in front of it.

A bike rental composes these one way. A car-pool composes them another. A washing-machine slot composes them a third. The composition is what makes a vertical; the primitives are what make a protocol.

What this is not.

DaiZen is not trying to be one large rental marketplace with every category in a drop-down. The world has had several attempts at that shape and it tends to end the same way: a custodian in the middle, a take-rate that climbs, a support queue in another time zone, and a slow drift away from the neighbours the product was first written for.

The layer beneath those marketplaces is what we are building. The escrow, the agreement, the receipt, the guild — the few pieces that genuinely need to be neutral. What sits on top can be local. A bike co-op in Kreis 4. A car-pool board for one office park. A residents' association running the laundry. A small agency specialising in semester-long sublets in Wiedikon. None of them have to ask a global platform for permission to exist. None of them have to give a global platform a cut.

The plumbing is general. The neighbourhoods are not. The contract holds, the street decides, and the value stays where it was made.