We've had a home-brewed solution for a while. PendingNotification(s) that get processed by a cron task that runs every minute. The PendingNotification has all t

We've had a home-brewed solution for a while. PendingNotification(s) that get processed by a cron task that runs every minute. The PendingNotification has all the data the cron task needs to execute it. Actually, for a while, GAE didn't even have cron tasks. So we were kicking off stuff using silent ajax calls from clients.