[losfair]

- Both FDB record layer and RefineDB support complex types and indexes (with the details differing a lot); FDB record layer's index support is more complete for now.

- FDB record layer is more mature and well-tested.

- RefineDB supports KV backends other than FoundationDB.

- RefineDB can run either as a server or an embedded library in user applications; FDB record layer is a Java-only library.

- RefineDB has a functional query language for complex queries; FDB record layer does not and provides a query API instead that allows to scan, filter and sort across records.