How can I subscribe to messages using Python/PHP/other REST-only SDKs?

Ably offers REST-only SDKs for Python and PHP. However, there are many ways to implement realtime features in those languages or corresponding frameworks.

1. You can use the MQTT protocol adapter, which translates back and forth between MQTT and Ably’s own protocol, allowing for seamless integration with any frameworks you'd like to use.

2. You can use a PubNub SDK with Ably over the PubNub protocol adapter, which again internally translates back to Ably's own protocol.

3. Or, if you wish to subscribe to messages and process them server-side, you should consider using the Reactor, which offers many ways to consume messages in real time, including support for AMQP and STOMP (there are Python and PHP libraries availabe for both).