Which DAML integrations (besides Canton) support multiple participants?
To answer that question, we first have to establish what we mean by a participant. Even going with the definition in the docs, the DAML Sandbox can be run with multiple participants, all using the same SQL Ledger backend. Going purely by that docs definition, you could even argue that mirroring the Ledger API on several ports would count as “several participants”, but that’s clearly not in the spirit of your question.
So let’s rather talk about the different topologies different ledgers have:
Sandbox Classic has what the docs call a fully centralized topology.
Sandbox goes one step further by separating the participant cleanly from the underlying SQL ledger so it could in theory be run with multiple participants. This topology is described under Scaling in the docs. The more centralized commercial offerings like DAML on Aurora and DAML on QLDB also have such a topology.
Many of the integrations with other DLT technologies use the Replication topology. Here, there are gradations with respect to the privacy between the replicas and participants, and between the replicas. The open source DAML on Fabric distribution is a good example of this topology, but so are the integrations with VMware Blockchain, Sawtooth, Besu and FISCO BCOS.
Canton and DAML on Corda use the Partitioned topology.