It looks a lot like a CvRDT (i.e. a state-based CRDT).

They describe it as a commutative monoid, which means it has associativity and commutativity. CvRDTs also need idempotence, so they can handle duplicate data. Either they are idempotent too (which would make it semilattice-like), or the network protocol handles the deduplication outside of the data itself.

Letting the payload/application define the merge operation is clever. I assume it would mean contracts could opt in to idempotency if it doesn't already exist.

The other bit Freenet has added is doing all this with DHT routing and subscriptions, rather than a more basic peer mesh. This is very different to a blockchain and means it probably isn't suited for anything transactional.

This is broadly correct.

> CvRDTs also need idempotence, so they can handle duplicate data. Either they are idempotent too (which would make it semilattice-like), or the network protocol handles the deduplication outside of the data itself.

Freenet's summary/delta synchronization mechanism implicitly disregards duplicate updates. The idea is that a peer A creates a "summary" of a contract's state which is sent to the other peer B which then creates a "delta", which contains anything in B's state that isn't in A's state. The delta is then sent from B to A bringing A's state up-to-date. Thus the contract defines a custom synchronization mechanism for its state which can be very efficient.

These summaries and deltas are just arbitrary bytes as far as the framework is concerned, their meaning is entirely up to the contract.

> The other bit Freenet has added is doing all this with DHT routing and subscriptions, rather than a more basic peer mesh. This is very different to a blockchain and means it probably isn't suited for anything transactional.

That's correct, Freenet doesn't guarantee a global consensus although in practice contract states will converge within a few seconds. This is good enough for applications like group chat and social networks but for a cryptocurrency you still need to solve the double-spend and global ordering problems.