Celery is an asynchronous task queue/job queue based on distributed message passing. It is focused on real-time operation, but supports scheduling as well.

The execution units, called tasks, are executed concurrently on a single or more worker servers. Tasks can execute asynchronously (in the background) or synchronously (wait until ready).

Celery is already used in production to process millions of tasks a day.

Celery is written in Python, but the protocol can be implemented in any language. It can also operate with other languages using webhooks.