SUP (Simple Update Protocol) is a simple and compact "ping feed" that web services can produce in order to alert the consumers of their feeds when a feed has been updated.
Django maintenance mode is a middleware that allows you to temporary shutdown your site for non staff users and show them a page that the site is down for maintenance. Logged in users having staff credentials can still fully use the site.
MMM (MySQL Master-Master Replication Manager) is set of flexible scripts to perform monitoring/failover and management of MySQL Master-Master replication cluster configurations.