- LiteSync directly competes with Marmot and supports DDL sync, but is closed source commercial (similar to SQLite EE): https://litesync.io
- dqlite is Canonical's distributed SQLite that depends on c-raft and kernel-level async I/O: https://dqlite.io
- cr-sqlite is a Rust-based loadable extension that adds CRDT changeset generation and reconciliation to SQLite: https://github.com/vlcn-io/cr-sqlite
Slightly related but not really (no multi writer, no C-level SQLite API or other restrictions):
- comdb2 (Bloombergs multi-homed RDBMS using SQLite as the frontend)
- rqlite: RDBMS with HTTP API and SQLite as the storage engine, used for replication and strong consistency (does not scale writes)
- litestream/LiteFS: disaster recovery replication
- liteserver: active read-only replication (predecessor of LiteSync)