Instant messaging server. Backend in pure Go (license GPL 3.0), client-side binding in Java, Javascript, and Swift, as well as gRPC client support for C++, C#, Go, Java, Node, PHP, Python, Ruby, Objective-C, etc. (license Apache 2.0). Wire transport is JSON over websocket (long polling is also available) for custom bindings, or protobuf with gRPC. Persistent storage is any one of RethinkDB, MySQL or MongoDB. A third-party unsupported DynamoDB adapter also exists. Other databases can...