We've just released Synapse 0.23 - which contains a bunch of significant performance improvements, bug and stability fixes - as well as a few new features: basic spam checking (the ability to configure your homeserver to reject events which match arbitrary rules, both from users and other servers) - and long-awaited support for privacy-preserving ('event_id_only') push notifications. This means that apps can choose to register themselves to receive push notifications which do not contain any information about the actual push, but instead act as a simple "wake up!" event, which triggers the app to then sync via the client-server API in order to display the actual push notification details. This is particularly useful for push notifications for E2E encrypted rooms, as it means the client has a chance of decrypting the message in order to display the push notification details in the UI (if the user wants that). matrix-ios-sdk and matrix-android-sdk are in the process of being moved over to use the new 'event_id_only' push format.
Long-awaited Communities/Groups will land in Synapse 0.24, which should come quite soon (we're almost ready to merge it to develop, but it's a major update so we wanted to get 0.23 out the door first).
As always, you can get your latest Synapse from https://github.com/matrix-org/synapse or a OS repository of your choice (we've just released the official Debian packages).